diff --git a/sagemaker-core/src/sagemaker/core/utils/utils.py b/sagemaker-core/src/sagemaker/core/utils/utils.py
index 8a8d90be6e..75a77cfa78 100644
--- a/sagemaker-core/src/sagemaker/core/utils/utils.py
+++ b/sagemaker-core/src/sagemaker/core/utils/utils.py
@@ -273,7 +273,8 @@ def pascal_to_snake(pascal_str):
 
 
 def is_not_primitive(obj):
-    return not isinstance(obj, (int, float, str, bool, datetime.datetime))
+    return not isinstance(obj, (int, float, str, bool, bytes, datetime.datetime))
+
 
 
 def is_not_str_dict(obj):
@@ -285,7 +286,8 @@ def is_primitive_list(obj):
 
 
 def is_primitive_class(cls):
-    return cls in (str, int, bool, float, datetime.datetime)
+    return cls in (str, int, bool, float, bytes, datetime.datetime)
+
 
 
 class Unassigned:
diff --git a/sagemaker-core/tests/unit/generated/test_utils.py b/sagemaker-core/tests/unit/generated/test_utils.py
index 44856d17d5..e9454c64af 100644
--- a/sagemaker-core/tests/unit/generated/test_utils.py
+++ b/sagemaker-core/tests/unit/generated/test_utils.py
@@ -373,6 +373,31 @@ def test_serialize_method_nested_shape():
     }
 
 
+
+def test_serialize_with_bytes_value_returns_bytes():
+    result = serialize({"body": b"1"})
+    assert result == {"body": b"1"}
+
+
+def test_serialize_with_empty_bytes_returns_empty_dict():
+    # Empty bytes is falsy, so the walrus operator in _serialize_dict skips it
+    result = serialize({"body": b""})
+    assert result == {}
+
+
+def test_serialize_with_bytes_in_list():
+    result = serialize([b"hello", b"world"])
+    assert result == [b"hello", b"world"]
+
+
+def test_is_not_primitive_with_bytes_returns_false():
+    assert is_not_primitive(b"test") is False
+
+
+def test_is_primitive_class_with_bytes_returns_true():
+    assert is_primitive_class(bytes) is True
+
+
 class TestUnassignedBehavior:
     """Test Unassigned class methods for proper behavior.