diff --git a/mlrun/runtimes/serving.py b/mlrun/runtimes/serving.py
index cf6ca2f02a0..2b71d6df2e1 100644
--- a/mlrun/runtimes/serving.py
+++ b/mlrun/runtimes/serving.py
@@ -106,6 +106,7 @@ def __init__(
         error_stream=None,
         track_models=None,
         secret_sources=None,
+        default_content_type=None,
     ):
 
         super().__init__(
@@ -145,6 +146,7 @@ def __init__(
         self.error_stream = error_stream
         self.track_models = track_models
         self.secret_sources = secret_sources or []
+        self.default_content_type = default_content_type
 
     @property
     def graph(self) -> Union[RouterStep, RootFlowStep]:
@@ -463,6 +465,7 @@ def _get_runtime_env(self):
             "graph_initializer": self.spec.graph_initializer,
             "error_stream": self.spec.error_stream,
             "track_models": self.spec.track_models,
+            "default_content_type": self.spec.default_content_type,
         }
 
         if self.spec.secret_sources:
@@ -492,6 +495,7 @@ def to_mock_server(
             track_models=self.spec.track_models,
             function_uri=self._function_uri(),
             secret_sources=self.spec.secret_sources,
+            default_content_type=self.spec.default_content_type,
             **kwargs,
         )
         server.init_states(
diff --git a/mlrun/serving/server.py b/mlrun/serving/server.py
index 5e087a787f6..3b94acc1a05 100644
--- a/mlrun/serving/server.py
+++ b/mlrun/serving/server.py
@@ -81,6 +81,7 @@ def __init__(
         error_stream=None,
         track_models=None,
         secret_sources=None,
+        default_content_type=None,
     ):
         self._graph = None
         self.graph: Union[RouterStep, RootFlowStep] = graph
@@ -100,6 +101,7 @@ def __init__(
         self._secrets = SecretsStore.from_list(secret_sources)
         self._db_conn = None
         self.resource_cache = None
+        self.default_content_type = default_content_type
 
     def set_current_function(self, function):
         """set which child function this server is currently running on"""
@@ -213,6 +215,14 @@ def run(self, event, context=None, get_body=False, extra_args=None):
         server_context = self.context
         context = context or server_context
         try:
+            if not event.content_type and self.default_content_type:
+                event.content_type = self.default_content_type
+            if (
+                isinstance(event.body, (str, bytes))
+                and event.content_type
+                and event.content_type in ["json", "application/json"]
+            ):
+                event.body = json.loads(event.body)
             response = self.graph.run(event, **(extra_args or {}))
         except Exception as exc:
             message = str(exc)
diff --git a/mlrun/serving/states.py b/mlrun/serving/states.py
index c256152c148..fe005ba34fd 100644
--- a/mlrun/serving/states.py
+++ b/mlrun/serving/states.py
@@ -1157,7 +1157,11 @@ def do_event(self, event):
             raise RuntimeError(f"bad function response {resp.text}")
 
         data = resp.content
-        if self.format == "json" or resp.headers["content-type"] == "application/json":
+        if (
+            self.format == "json"
+            or resp.headers["content-type"] == "application/json"
+            and isinstance(data, (str, bytes))
+        ):
             data = json.loads(data)
         event.body = data
         return event
diff --git a/tests/serving/test_flow.py b/tests/serving/test_flow.py
index 11d59357720..80958a26451 100644
--- a/tests/serving/test_flow.py
+++ b/tests/serving/test_flow.py
@@ -109,3 +109,34 @@ def test_on_error():
     logger.info(f"flow: {graph.to_yaml()}")
     resp = server.test(body=[])
     assert resp["error"] and resp["origin_state"] == "raiser", "error wasnt caught"
+
+
+def return_type(event):
+    return event.__class__.__name__
+
+
+def test_content_type():
+    fn = mlrun.new_function("tests", kind="serving")
+    graph = fn.set_topology("flow", engine="sync")
+    graph.to(name="totype", handler=return_type)
+    server = fn.to_mock_server()
+
+    # test that we json.load() when the content type is json
+    resp = server.test(body={"a": 1})
+    assert resp == "dict", "invalid type"
+    resp = server.test(body="[1,2]")
+    assert resp == "str", "invalid type"
+    resp = server.test(body={"a": 1}, content_type="application/json")
+    assert resp == "dict", "invalid type"
+    resp = server.test(body="[1,2]", content_type="application/json")
+    assert resp == "list", "did not load json"
+
+    # test the use of default content type
+    fn = mlrun.new_function("tests", kind="serving")
+    fn.spec.default_content_type = "application/json"
+    graph = fn.set_topology("flow", engine="sync")
+    graph.to(name="totype", handler=return_type)
+
+    server = fn.to_mock_server()
+    resp = server.test(body="[1,2]")
+    assert resp == "list", "did not load json"