diff --git a/src/anthropic/lib/bedrock/_client.py b/src/anthropic/lib/bedrock/_client.py
index cda0690df..e9ea0c112 100644
--- a/src/anthropic/lib/bedrock/_client.py
+++ b/src/anthropic/lib/bedrock/_client.py
@@ -67,17 +67,17 @@ def _prepare_options(input_options: FinalRequestOptions) -> FinalRequestOptions:
     return options
 
 
-def _infer_region() -> str:
+def _infer_region(aws_profile: str | None = None) -> str:
     """
     Infer the AWS region from the environment variables or
     from the boto3 session if available.
     """
-    aws_region = os.environ.get("AWS_REGION")
+    aws_region = os.environ.get("AWS_REGION") or os.environ.get("AWS_DEFAULT_REGION")
     if aws_region is None:
         try:
             import boto3
 
-            session = boto3.Session()
+            session = boto3.Session(profile_name=aws_profile)
             if session.region_name:
                 aws_region = session.region_name
         except ImportError:
@@ -178,7 +178,7 @@ def __init__(
 
         self.aws_access_key = aws_access_key
 
-        self.aws_region = _infer_region() if aws_region is None else aws_region
+        self.aws_region = _infer_region(aws_profile) if aws_region is None else aws_region
         self.aws_profile = aws_profile
 
         self.aws_session_token = aws_session_token
@@ -343,7 +343,7 @@ def __init__(
 
         self.aws_access_key = aws_access_key
 
-        self.aws_region = _infer_region() if aws_region is None else aws_region
+        self.aws_region = _infer_region(aws_profile) if aws_region is None else aws_region
         self.aws_profile = aws_profile
 
         self.aws_session_token = aws_session_token
diff --git a/tests/lib/test_bedrock.py b/tests/lib/test_bedrock.py
index 6e45c27f7..2d33fa932 100644
--- a/tests/lib/test_bedrock.py
+++ b/tests/lib/test_bedrock.py
@@ -246,6 +246,13 @@ def test_api_key_env_mutual_exclusion(monkeypatch: t.Any) -> None:
         )
 
 
+def test_region_infer_from_aws_default_region_env(monkeypatch: t.Any) -> None:
+    monkeypatch.setenv("AWS_DEFAULT_REGION", "ap-southeast-1")
+    monkeypatch.delenv("AWS_REGION", raising=False)
+    client = AnthropicBedrock()
+    assert client.aws_region == "ap-southeast-1"
+
+
 def test_region_infer_from_profile(
     mock_aws_config: None,  # noqa: ARG001
     profiles: t.List[AwsConfigProfile],
@@ -275,3 +282,23 @@ def test_region_infer_from_specified_profile(
     client = AnthropicBedrock()
 
     assert client.aws_region == next(profile for profile in profiles if profile["name"] == aws_profile)["region"]
+
+
+@pytest.mark.parametrize(
+    "profiles, aws_profile",
+    [
+        pytest.param(
+            [{"name": "default", "region": "us-east-2"}, {"name": "custom", "region": "us-west-1"}],
+            "custom",
+            id="custom profile via aws_profile arg",
+        ),
+    ],
+)
+def test_region_infer_from_aws_profile_arg(
+    mock_aws_config: None,  # noqa: ARG001
+    profiles: t.List[AwsConfigProfile],
+    aws_profile: str,
+) -> None:
+    client = AnthropicBedrock(aws_profile=aws_profile)
+
+    assert client.aws_region == next(profile for profile in profiles if profile["name"] == aws_profile)["region"]