diff --git a/build-scripts/ubuntu-2004/build-3rd-parties.sh b/build-scripts/ubuntu-2004/build-3rd-parties.sh
index b8aef2358f..97f4f07e1b 100755
--- a/build-scripts/ubuntu-2004/build-3rd-parties.sh
+++ b/build-scripts/ubuntu-2004/build-3rd-parties.sh
@@ -126,4 +126,3 @@ build_from_pypi semver 2.13.0
 build_from_pypi sha3
 build_from_pypi six
 build_from_pypi sortedcontainers 1.5.7
-build_from_pypi ujson 1.33
diff --git a/build-scripts/ubuntu-2004/prepare-package.sh b/build-scripts/ubuntu-2004/prepare-package.sh
index 7579ccf81d..44eacc88a4 100755
--- a/build-scripts/ubuntu-2004/prepare-package.sh
+++ b/build-scripts/ubuntu-2004/prepare-package.sh
@@ -29,7 +29,6 @@ if [ "$distro_packages" = "debian-packages" ]; then
   # Update the package names to match the versions that are pre-installed on the os.
   echo -e "\nAdapt the dependencies for the Canonical archive"
   #### ToDo adjust packages for the Cannonical archive for Ubuntu 20.04 (focal)
-  # sed -i "s~ujson==1.33~ujson==1.33-1build1~" setup.py
   # sed -i "s~prompt_toolkit==0.57~prompt_toolkit==0.57-1~" setup.py
   # sed -i "s~msgpack-python==0.4.6~msgpack==0.4.6-1build1~" setup.py
 elif [ "$distro_packages" = "python-packages" ]; then
diff --git a/common/serializers/json_serializer.py b/common/serializers/json_serializer.py
index a012dbe0cd..71fa03da9b 100644
--- a/common/serializers/json_serializer.py
+++ b/common/serializers/json_serializer.py
@@ -2,45 +2,27 @@
 
 
 import base64
+import json
 from typing import Dict
 
 from common.serializers.mapping_serializer import MappingSerializer
 
-try:
-    import ujson as json
-    from ujson import encode as uencode
 
-    # Older versions of ujson's encode do not support `sort_keys`, if that
-    # is the case default to using json
-    uencode({'xx': '123', 'aa': 90}, sort_keys=True)
+class OrderedJsonEncoder(json.JSONEncoder):
+    def __init__(self, *args, **kwargs):
+        kwargs['ensure_ascii'] = False
+        kwargs['sort_keys'] = True
+        kwargs['separators'] = (',', ':')
+        super().__init__(*args, **kwargs)
 
-    class UJsonEncoder:
-        @staticmethod
-        def encode(o):
-            if isinstance(o, (bytes, bytearray)):
-                return '"{}"'.format(base64.b64encode(o).decode("utf-8"))
-            else:
-                return uencode(o, sort_keys=True)
+    def encode(self, o):
+        if isinstance(o, (bytes, bytearray)):
+            return '"{}"'.format(base64.b64encode(o).decode("utf-8"))
+        else:
+            return super().encode(o)
 
-    JsonEncoder = UJsonEncoder()
 
-except (ImportError, TypeError):
-    import json
-
-    class OrderedJsonEncoder(json.JSONEncoder):
-        def __init__(self, *args, **kwargs):
-            kwargs['ensure_ascii'] = False
-            kwargs['sort_keys'] = True
-            kwargs['separators'] = (',', ':')
-            super().__init__(*args, **kwargs)
-
-        def encode(self, o):
-            if isinstance(o, (bytes, bytearray)):
-                return '"{}"'.format(base64.b64encode(o).decode("utf-8"))
-            else:
-                return super().encode(o)
-
-    JsonEncoder = OrderedJsonEncoder()
+JsonEncoder = OrderedJsonEncoder()
 
 
 class JsonSerializer(MappingSerializer):
diff --git a/common/serializers/signing_serializer.py b/common/serializers/signing_serializer.py
index 4888cb5f46..6ab526f8e3 100644
--- a/common/serializers/signing_serializer.py
+++ b/common/serializers/signing_serializer.py
@@ -90,6 +90,3 @@ def serialize(self, obj, level=0, objname=None, topLevelKeysToIgnore=None,
             return res
 
         return res.encode('utf-8')
-
-        # topLevelKeysToIgnore = topLevelKeysToIgnore or []
-        # return ujson.dumps({k:obj[k] for k in obj.keys() if k not in topLevelKeysToIgnore}, sort_keys=True)
diff --git a/common/test/test_json_serializer_ujson_compat.py b/common/test/test_json_serializer_ujson_compat.py
new file mode 100644
index 0000000000..2a5eb8cacb
--- /dev/null
+++ b/common/test/test_json_serializer_ujson_compat.py
@@ -0,0 +1,73 @@
+"""
+Regression tests added when the ``ujson`` dependency was removed: pin the
+exact byte output of ``JsonSerializer`` (sorted keys, compact separators,
+raw UTF-8), since it feeds signing/hashing and must stay byte-stable.
+"""
+import pytest
+
+from common.serializers.json_serializer import JsonSerializer
+
+
+@pytest.fixture
+def sz():
+    return JsonSerializer()
+
+
+def test_keys_sorted_and_compact(sz):
+    # Insertion order must not affect output; keys are sorted, no whitespace.
+    assert sz.serialize({'b': 2, 'a': 1, 'c': 3}, toBytes=False) == '{"a":1,"b":2,"c":3}'
+
+
+def test_non_ascii_kept_raw_utf8(sz):
+    # ensure_ascii=False: characters are emitted as raw UTF-8, not \\uXXXX.
+    assert sz.serialize({'name': 'héllo', 'kr': '한글', 'emoji': '🚀'},
+                        toBytes=False) == '{"emoji":"🚀","kr":"한글","name":"héllo"}'
+    # And the bytes form is the UTF-8 encoding of that string.
+    assert sz.serialize({'name': 'héllo'}) == '{"name":"héllo"}'.encode('utf-8')
+
+
+def test_float_repr_pinned(sz):
+    assert sz.serialize({'a': 14.8639, 'b': -97.466179, 'c': 1.0, 'd': 1e20},
+                        toBytes=False) == '{"a":14.8639,"b":-97.466179,"c":1.0,"d":1e+20}'
+
+
+def test_int_keys_become_strings(sz):
+    # json coerces non-string keys to strings and then sorts lexicographically.
+    assert sz.serialize({3: 'c', 1: 'a', 2: 'b'}, toBytes=False) == '{"1":"a","2":"b","3":"c"}'
+
+
+def test_bool_and_none(sz):
+    assert sz.serialize({'t': True, 'f': False, 'n': None},
+                        toBytes=False) == '{"f":false,"n":null,"t":true}'
+
+
+def test_empty_dict(sz):
+    assert sz.serialize({}, toBytes=False) == '{}'
+
+
+def test_top_level_bytes_base64(sz):
+    # The OrderedJsonEncoder.encode override base64-encodes a top-level
+    # bytes/bytearray value (b'raw' -> base64 'cmF3').
+    assert sz.serialize(b'raw', toBytes=False) == '"cmF3"'
+    assert sz.serialize(bytearray(b'raw'), toBytes=False) == '"cmF3"'
+
+
+def test_round_trip(sz):
+    data = {'name': 'Alice', 'n': 1, 'f': 1.5, 'b': True, 'list': [1, 'two', None]}
+    assert sz.deserialize(sz.serialize(data)) == data
+    assert sz.deserialize(sz.serialize(data, toBytes=False)) == data
+
+
+@pytest.mark.parametrize('value', [
+    {'z': b'raw'},      # bytes nested in a dict value
+    [b'raw'],           # bytes nested in a list
+    {'z': bytearray(b'raw')},
+])
+def test_nested_bytes_raise_typeerror(sz, value):
+    """
+    The bytes special-case in ``OrderedJsonEncoder.encode`` only fires for a
+    top-level value; bytes nested in a container raise TypeError. A fix, if
+    ever needed, belongs in ``OrderedJsonEncoder.default``.
+    """
+    with pytest.raises(TypeError):
+        sz.serialize(value)
diff --git a/dev-setup/ubuntu/ubuntu-2004/SetupVMTest.txt b/dev-setup/ubuntu/ubuntu-2004/SetupVMTest.txt
index b905bd140e..0eca41813f 100644
--- a/dev-setup/ubuntu/ubuntu-2004/SetupVMTest.txt
+++ b/dev-setup/ubuntu/ubuntu-2004/SetupVMTest.txt
@@ -82,7 +82,6 @@
             sortedcontainers==1.5.7 \
             timeout-decorator==0.5.0 \
             toml==0.10.2 \
-            ujson==1.33 \
             wcwidth==0.2.5 \
             wheel==0.34.2 \
             zipp==1.2.0
diff --git a/ledger/test/helper.py b/ledger/test/helper.py
index a1a2194e55..548a9a6ae6 100644
--- a/ledger/test/helper.py
+++ b/ledger/test/helper.py
@@ -108,7 +108,6 @@ def create_ledger_rocksdb_storage(txn_serializer, hash_serializer, tempdir, init
 
 
 def create_ledger_chunked_file_storage(txn_serializer, hash_serializer, tempdir, init_genesis_txn_file=None):
-    chunk_creator = None
     db_name = 'transactions'
     if isinstance(txn_serializer, MsgPackSerializer):
         # TODO: fix chunk_creator support
@@ -119,6 +118,8 @@ def chunk_creator(name):
                                                   isLineNoKey=True,
                                                   storeContentHash=False,
                                                   ensureDurability=False)
+    else:
+        chunk_creator = None
     store = ChunkedFileStore(tempdir,
                              db_name,
                              isLineNoKey=True,
diff --git a/plenum/common/channel.py b/plenum/common/channel.py
index de782ca6aa..70eb36f842 100644
--- a/plenum/common/channel.py
+++ b/plenum/common/channel.py
@@ -156,7 +156,7 @@ def _process_sync(self, msg: Any):
         # This is done so that messages can include additional metadata
         # isinstance is not used here because it returns true for NamedTuple
         # as well.
-        if type(msg) != tuple:
+        if type(msg) is not tuple:
             msg = (msg,)
         handler = self._find_handler(msg[0])
         if handler is None:
diff --git a/plenum/common/util.py b/plenum/common/util.py
index ea44ef9206..8f6fd3a082 100644
--- a/plenum/common/util.py
+++ b/plenum/common/util.py
@@ -342,6 +342,14 @@ def z85_to_friendly(z):
         return z
 
 
+def json_default_bytes_to_str(obj):
+    """``json.dumps`` default hook decoding bytes/bytearray as UTF-8."""
+    if isinstance(obj, (bytes, bytearray)):
+        return obj.decode()
+    raise TypeError('Object of type {} is not JSON '
+                    'serializable'.format(type(obj).__name__))
+
+
 def runWithLoop(loop, callback, *args, **kwargs):
     if loop.is_running():
         loop.call_soon(asyncio.ensure_future, callback(*args, **kwargs))
diff --git a/plenum/recorder/recorder.py b/plenum/recorder/recorder.py
index ca897d9f33..1003caae66 100644
--- a/plenum/recorder/recorder.py
+++ b/plenum/recorder/recorder.py
@@ -1,14 +1,11 @@
 import os
 import time
+import json
 from typing import Callable
 
+from plenum.common.util import json_default_bytes_to_str
 from storage.kv_store_rocksdb_int_keys import KeyValueStorageRocksdbIntKeys
 
-try:
-    import ujson as json
-except ImportError:
-    import json
-
 
 class Recorder:
     INCOMING_FLAG = 0
@@ -50,7 +47,8 @@ def add_to_store(self, key, val):
             existing = json.loads(existing)
         except KeyError:
             existing = []
-        self.store.put(key, json.dumps([*existing, val]))
+        self.store.put(key, json.dumps([*existing, val],
+                                       default=json_default_bytes_to_str))
 
     def register_replay_target(self, id, target: Callable):
         assert id not in self.replay_targets
diff --git a/plenum/server/plugin/stats_consumer/plugin_firebase_stats_consumer.py b/plenum/server/plugin/stats_consumer/plugin_firebase_stats_consumer.py
index 1fab98b30f..6bf2f4a45e 100644
--- a/plenum/server/plugin/stats_consumer/plugin_firebase_stats_consumer.py
+++ b/plenum/server/plugin/stats_consumer/plugin_firebase_stats_consumer.py
@@ -6,11 +6,11 @@
 from plenum.common.types import EVENT_PERIODIC_STATS_THROUGHPUT, \
     EVENT_NODE_STARTED, EVENT_REQ_ORDERED, EVENT_PERIODIC_STATS_LATENCIES, \
     PLUGIN_TYPE_STATS_CONSUMER, EVENT_VIEW_CHANGE, EVENT_PERIODIC_STATS_NODES, \
-    EVENT_PERIODIC_STATS_TOTAL_REQUESTS, EVENT_PERIODIC_STATS_NODE_INFO,\
+    EVENT_PERIODIC_STATS_TOTAL_REQUESTS, EVENT_PERIODIC_STATS_NODE_INFO, \
     EVENT_PERIODIC_STATS_SYSTEM_PERFORMANCE_INFO
 from stp_core.common.log import getlogger
 from plenum.config import STATS_SERVER_IP, STATS_SERVER_PORT, STATS_SERVER_MESSAGE_BUFFER_MAX_SIZE
-from plenum.server.plugin.stats_consumer.stats_publisher import StatsPublisher,\
+from plenum.server.plugin.stats_consumer.stats_publisher import StatsPublisher, \
     Topic
 from plenum.server.plugin_loader import HasDynamicallyImportedModules
 from plenum.server.stats_consumer import StatsConsumer
diff --git a/plenum/test/recorder/test_recorder.py b/plenum/test/recorder/test_recorder.py
index 29d85aa26f..5eef608377 100644
--- a/plenum/test/recorder/test_recorder.py
+++ b/plenum/test/recorder/test_recorder.py
@@ -1,14 +1,10 @@
 import random
 import time
+import json
 from collections import OrderedDict
 
 from plenum.common.util import randomString
 
-try:
-    import ujson as json
-except ImportError:
-    import json
-
 import pytest
 
 from plenum.recorder.recorder import Recorder
@@ -60,6 +56,19 @@ def test_add_to_recorder(recorder):
         i += 1
 
 
+def test_add_to_recorder_with_bytes(recorder):
+    msg1, frm1 = b'{"msg": "m1"}', b'f1'
+    msg2, to1 = b'{"msg": "m2"}', 't1'
+    recorder.add_incoming(msg1, frm1)
+    recorder.add_outgoing(msg2, to1)
+
+    all_msgs = []
+    for _, v in recorder.store.iterator(include_value=True):
+        all_msgs.extend(Recorder.get_parsed(v))
+    assert Recorder.filter_incoming(all_msgs) == [['{"msg": "m1"}', 'f1']]
+    assert Recorder.filter_outgoing(all_msgs) == [['{"msg": "m2"}', 't1']]
+
+
 def test_get_list_from_recorder(recorder):
     msg1, frm1 = 'm1', 'f1'
     msg2, frm2 = 'm2', 'f2'
diff --git a/scripts/test_zmq/test_zmq/zstack.py b/scripts/test_zmq/test_zmq/zstack.py
index f80b818235..73ed6ccd64 100644
--- a/scripts/test_zmq/test_zmq/zstack.py
+++ b/scripts/test_zmq/test_zmq/zstack.py
@@ -1,10 +1,5 @@
 from test_zmq.authenticator import MultiZapAuthenticator
-
-try:
-    import ujson as json
-except ImportError:
-    import json
-
+import json
 import os
 import shutil
 import sys
@@ -561,7 +556,7 @@ def transmit(self, msg, uid, timeout=None, serialized=False, is_batch=False):
     @staticmethod
     def serializeMsg(msg):
         if isinstance(msg, Mapping):
-            msg = json.dumps(msg)
+            msg = json.dumps(msg, separators=(',', ':'))
         if isinstance(msg, str):
             msg = msg.encode()
         assert isinstance(msg, bytes)
diff --git a/setup.py b/setup.py
index 87925e7837..035f345447 100644
--- a/setup.py
+++ b/setup.py
@@ -131,8 +131,6 @@ def run(self):
                         'six',
                         ### Tests fail without version pin (GHA run: https://github.com/udosson/indy-plenum/actions/runs/1078741118)
                         'sortedcontainers==1.5.7',
-                        ### Tests fail without version pin (GHA run: https://github.com/udosson/indy-plenum/actions/runs/1078741118)
-                        'ujson==1.33',
                         ],
 
     setup_requires=['pytest-runner==5.3.0'],
diff --git a/stp_zmq/zstack.py b/stp_zmq/zstack.py
index 32a2a07f60..19df6bd444 100644
--- a/stp_zmq/zstack.py
+++ b/stp_zmq/zstack.py
@@ -1,4 +1,5 @@
 import inspect
+import json
 
 from plenum.common.constants import OP_FIELD_NAME, BATCH
 from plenum.common.metrics_collector import NullMetricsCollector
@@ -8,10 +9,6 @@
 from stp_core.common.constants import CONNECTION_PREFIX, ZMQ_NETWORK_PROTOCOL
 from stp_zmq.client_message_provider import ClientMessageProvider
 
-try:
-    import ujson as json
-except ImportError:
-    import json
 
 import os
 import shutil
@@ -871,7 +868,7 @@ def transmit(self, msg, uid, timeout=None, serialized=False, is_batch=False):
     @staticmethod
     def serializeMsg(msg):
         if isinstance(msg, Mapping):
-            msg = json.dumps(msg)
+            msg = json.dumps(msg, separators=(',', ':'))
         if isinstance(msg, str):
             msg = msg.encode()
         assert isinstance(msg, bytes)