diff --git a/src/msgraph_core/_enums.py b/src/msgraph_core/_enums.py
index 5f217fe8..74918f15 100644
--- a/src/msgraph_core/_enums.py
+++ b/src/msgraph_core/_enums.py
@@ -4,7 +4,7 @@
 # ------------------------------------
 #pylint: disable=invalid-name
 
-from enum import Enum
+from enum import Enum, IntFlag
 
 
 class APIVersion(str, Enum):
@@ -16,7 +16,7 @@ def __str__(self):
         return self.value
 
 
-class FeatureUsageFlag(int, Enum):
+class FeatureUsageFlag(IntFlag):
     """Enumerated list of values used to flag usage of specific middleware"""
 
     NONE = 0
@@ -27,7 +27,7 @@ class FeatureUsageFlag(int, Enum):
     LOGGING_HANDLER_ENABLED = 16
 
     def __str__(self):
-        return self.value
+        return str(self.value)
 
 
 class NationalClouds(str, Enum):
diff --git a/tests/test_enums.py b/tests/test_enums.py
new file mode 100644
index 00000000..547883eb
--- /dev/null
+++ b/tests/test_enums.py
@@ -0,0 +1,114 @@
+"""Tests for msgraph_core._enums module."""
+from enum import Enum, IntFlag
+
+from msgraph_core._enums import APIVersion, FeatureUsageFlag, NationalClouds
+
+
+def test_feature_usage_flag_str_returns_string_type():
+    """__str__() must return str, not int (Python data model requirement)."""
+    for flag in FeatureUsageFlag:
+        result = str(flag)
+        assert isinstance(result, str), (
+            f"str({flag.name}) returned {type(result).__name__}, expected str"
+        )
+
+
+def test_feature_usage_flag_str_returns_numeric_value_as_string():
+    """__str__() should return the numeric value as a string."""
+    assert str(FeatureUsageFlag.NONE) == "0"
+    assert str(FeatureUsageFlag.REDIRECT_HANDLER_ENABLED) == "1"
+    assert str(FeatureUsageFlag.RETRY_HANDLER_ENABLED) == "2"
+    assert str(FeatureUsageFlag.AUTH_HANDLER_ENABLED) == "4"
+    assert str(FeatureUsageFlag.DEFAULT_HTTP_PROVIDER_ENABLED) == "8"
+    assert str(FeatureUsageFlag.LOGGING_HANDLER_ENABLED) == "16"
+
+
+def test_feature_usage_flag_is_intflag():
+    """FeatureUsageFlag should be an IntFlag for proper bitwise operations."""
+    assert issubclass(FeatureUsageFlag, IntFlag)
+
+
+def test_feature_usage_flag_is_int_instance():
+    """FeatureUsageFlag members should be instances of int."""
+    for flag in FeatureUsageFlag:
+        assert isinstance(flag, int)
+
+
+def test_feature_usage_flag_is_enum_instance():
+    """FeatureUsageFlag members should be instances of Enum."""
+    for flag in FeatureUsageFlag:
+        assert isinstance(flag, Enum)
+
+
+def test_feature_usage_flag_bitwise_or_returns_feature_usage_flag():
+    """Bitwise OR should return FeatureUsageFlag, not plain int."""
+    combined = FeatureUsageFlag.REDIRECT_HANDLER_ENABLED | FeatureUsageFlag.RETRY_HANDLER_ENABLED
+    assert isinstance(combined, FeatureUsageFlag)
+    assert combined.value == 3
+
+
+def test_feature_usage_flag_bitwise_and_returns_feature_usage_flag():
+    """Bitwise AND should return FeatureUsageFlag, not plain int."""
+    combined = FeatureUsageFlag.REDIRECT_HANDLER_ENABLED | FeatureUsageFlag.RETRY_HANDLER_ENABLED
+    result = combined & FeatureUsageFlag.REDIRECT_HANDLER_ENABLED
+    assert isinstance(result, FeatureUsageFlag)
+    assert result.value == 1
+
+
+def test_feature_usage_flag_bitwise_xor_returns_feature_usage_flag():
+    """Bitwise XOR should return FeatureUsageFlag, not plain int."""
+    combined = FeatureUsageFlag.REDIRECT_HANDLER_ENABLED | FeatureUsageFlag.RETRY_HANDLER_ENABLED
+    result = combined ^ FeatureUsageFlag.REDIRECT_HANDLER_ENABLED
+    assert isinstance(result, FeatureUsageFlag)
+    assert result.value == 2
+
+
+def test_feature_usage_flag_bitwise_invert_returns_feature_usage_flag():
+    """Bitwise invert should return FeatureUsageFlag, not plain int."""
+    result = ~FeatureUsageFlag.NONE
+    assert isinstance(result, FeatureUsageFlag)
+
+
+def test_feature_usage_flag_combined_flags_str():
+    """Combined flags should also return string from __str__()."""
+    combined = FeatureUsageFlag.REDIRECT_HANDLER_ENABLED | FeatureUsageFlag.RETRY_HANDLER_ENABLED
+    result = str(combined)
+    assert isinstance(result, str)
+    assert result == "3"
+
+
+def test_feature_usage_flag_values_are_powers_of_two():
+    """Flag values should be powers of 2 (except NONE=0) for proper bitmask behavior."""
+    assert FeatureUsageFlag.NONE.value == 0
+    assert FeatureUsageFlag.REDIRECT_HANDLER_ENABLED.value == 1
+    assert FeatureUsageFlag.RETRY_HANDLER_ENABLED.value == 2
+    assert FeatureUsageFlag.AUTH_HANDLER_ENABLED.value == 4
+    assert FeatureUsageFlag.DEFAULT_HTTP_PROVIDER_ENABLED.value == 8
+    assert FeatureUsageFlag.LOGGING_HANDLER_ENABLED.value == 16
+
+
+def test_api_version_str_returns_string_type():
+    """__str__() must return str."""
+    for version in APIVersion:
+        result = str(version)
+        assert isinstance(result, str)
+
+
+def test_api_version_str_returns_value():
+    """__str__() should return the enum value."""
+    assert str(APIVersion.beta) == "beta"
+    assert str(APIVersion.v1) == "v1.0"
+
+
+def test_national_clouds_str_returns_string_type():
+    """__str__() must return str."""
+    for cloud in NationalClouds:
+        result = str(cloud)
+        assert isinstance(result, str)
+
+
+def test_national_clouds_str_returns_url_value():
+    """__str__() should return the cloud URL."""
+    assert str(NationalClouds.Global) == "https://graph.microsoft.com"
+    assert str(NationalClouds.US_GOV) == "https://graph.microsoft.us"
+    assert str(NationalClouds.China) == "https://microsoftgraph.chinacloudapi.cn"