diff --git a/tests/v3/oauth/test_channel_access_token_query_params.py b/tests/v3/oauth/test_channel_access_token_query_params.py
new file mode 100644
index 000000000..c86b52632
--- /dev/null
+++ b/tests/v3/oauth/test_channel_access_token_query_params.py
@@ -0,0 +1,161 @@
+# -*- coding: utf-8 -*-
+
+#  Licensed under the Apache License, Version 2.0 (the "License"); you may
+#  not use this file except in compliance with the License. You may obtain
+#  a copy of the License at
+#
+#       https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#  License for the specific language governing permissions and limitations
+#  under the License.
+
+"""
+Regression tests verifying that query parameter names are sent as snake_case,
+not camelCase.
+"""
+
+import unittest
+from urllib.parse import parse_qs
+
+from pytest_httpserver.httpserver import HTTPServer
+
+from linebot.v3.oauth import (
+    ApiClient,
+    Configuration,
+    ChannelAccessToken,
+)
+
+
+class TestQueryParamNamesAreSnakeCase(unittest.TestCase):
+    """
+    Verify that GET endpoints send snake_case query keys to the LINE API,
+    not camelCase keys produced by the OpenAPI generator's paramName conversion.
+    """
+
+    def test_verify_channel_token_by_jwt_uses_snake_case_key(self):
+        """
+        verify_channel_token_by_jwt() must send `access_token=...` in the query
+        string, NOT `accessToken=...`.
+
+        Endpoint: GET /oauth2/v2.1/verify
+        """
+        dummy_access_token = "dummy_access_token_value"
+
+        expected_response = {
+            "client_id": "1234567890",
+            "expires_in": 3599,
+            "scope": "profile",
+        }
+
+        with HTTPServer() as httpserver:
+            httpserver.expect_request(
+                uri="/oauth2/v2.1/verify",
+                method="GET",
+            ).respond_with_json(expected_response, status=200)
+
+            configuration = Configuration(
+                host=httpserver.url_for("/")
+            )
+
+            with ApiClient(configuration) as api_client:
+                api = ChannelAccessToken(api_client)
+                api.verify_channel_token_by_jwt(access_token=dummy_access_token)
+
+            self.assertEqual(len(httpserver.log), 1)
+            req, _ = httpserver.log[0]
+
+            query_string = req.query_string.decode("utf-8")
+            parsed = parse_qs(query_string)
+
+            # snake_case key must be present
+            self.assertIn(
+                "access_token", parsed,
+                "Query string must contain 'access_token' (snake_case), "
+                f"but got: {query_string!r}"
+            )
+            self.assertEqual(parsed["access_token"], [dummy_access_token])
+
+            # camelCase key must NOT be present
+            self.assertNotIn(
+                "accessToken", parsed,
+                "Query string must NOT contain 'accessToken' (camelCase), "
+                f"but got: {query_string!r}"
+            )
+
+    def test_gets_all_valid_channel_access_token_key_ids_uses_snake_case_keys(self):
+        """
+        gets_all_valid_channel_access_token_key_ids() must send
+        `client_assertion_type=...` and `client_assertion=...` in the query
+        string, NOT `clientAssertionType=...` / `clientAssertion=...`.
+
+        Endpoint: GET /oauth2/v2.1/tokens/kid
+        """
+        dummy_client_assertion_type = (
+            "urn:ietf:params:oauth:client-assertion-type:jwt-bearer"
+        )
+        dummy_client_assertion = "eyJhbGciOiJSUzI1NiJ9.dummy.signature"
+
+        expected_response = {
+            "kids": ["key_id_1", "key_id_2"],
+        }
+
+        with HTTPServer() as httpserver:
+            httpserver.expect_request(
+                uri="/oauth2/v2.1/tokens/kid",
+                method="GET",
+            ).respond_with_json(expected_response, status=200)
+
+            configuration = Configuration(
+                host=httpserver.url_for("/")
+            )
+
+            with ApiClient(configuration) as api_client:
+                api = ChannelAccessToken(api_client)
+                api.gets_all_valid_channel_access_token_key_ids(
+                    client_assertion_type=dummy_client_assertion_type,
+                    client_assertion=dummy_client_assertion,
+                )
+
+            self.assertEqual(len(httpserver.log), 1)
+            req, _ = httpserver.log[0]
+
+            query_string = req.query_string.decode("utf-8")
+            parsed = parse_qs(query_string)
+
+            # snake_case keys must be present
+            self.assertIn(
+                "client_assertion_type", parsed,
+                "Query string must contain 'client_assertion_type' (snake_case), "
+                f"but got: {query_string!r}"
+            )
+            self.assertEqual(
+                parsed["client_assertion_type"], [dummy_client_assertion_type]
+            )
+
+            self.assertIn(
+                "client_assertion", parsed,
+                "Query string must contain 'client_assertion' (snake_case), "
+                f"but got: {query_string!r}"
+            )
+            self.assertEqual(
+                parsed["client_assertion"], [dummy_client_assertion]
+            )
+
+            # camelCase keys must NOT be present
+            self.assertNotIn(
+                "clientAssertionType", parsed,
+                "Query string must NOT contain 'clientAssertionType' (camelCase), "
+                f"but got: {query_string!r}"
+            )
+            self.assertNotIn(
+                "clientAssertion", parsed,
+                "Query string must NOT contain 'clientAssertion' (camelCase), "
+                f"but got: {query_string!r}"
+            )
+
+
+if __name__ == "__main__":
+    unittest.main()