diff --git a/hamilton/plugins/polars_post_1_0_0_extensions.py b/hamilton/plugins/polars_post_1_0_0_extensions.py
index dab1a3973..3df25674e 100644
--- a/hamilton/plugins/polars_post_1_0_0_extensions.py
+++ b/hamilton/plugins/polars_post_1_0_0_extensions.py
@@ -523,8 +523,9 @@ def _get_loading_kwargs(self):
 
     def load_data(self, type_: type) -> tuple[DATAFRAME_TYPE, dict[str, Any]]:
         df = pl.read_json(self.source, **self._get_loading_kwargs())
-        metadata = utils.get_file_metadata(self.source)
-        return df, metadata
+        if isinstance(self.source, (str, Path)):
+            return df, utils.get_file_metadata(self.source)
+        return df, utils.get_dataframe_metadata(df)
 
     @classmethod
     def name(cls) -> str:
@@ -549,7 +550,9 @@ def save_data(self, data: DATAFRAME_TYPE | pl.LazyFrame) -> dict[str, Any]:
             data = data.collect()
 
         data.write_json(self.file)
-        return utils.get_file_and_dataframe_metadata(self.file, data)
+        if isinstance(self.file, (str, Path)):
+            return utils.get_file_and_dataframe_metadata(self.file, data)
+        return utils.get_dataframe_metadata(data)
 
     @classmethod
     def name(cls) -> str:
@@ -581,8 +584,9 @@ def _get_loading_kwargs(self):
 
     def load_data(self, type_: type) -> tuple[DATAFRAME_TYPE, dict[str, Any]]:
         df = pl.read_ndjson(self.source, **self._get_loading_kwargs())
-        metadata = utils.get_file_metadata(self.source)
-        return df, metadata
+        if isinstance(self.source, (str, Path)):
+            return df, utils.get_file_metadata(self.source)
+        return df, utils.get_dataframe_metadata(df)
 
     @classmethod
     def name(cls) -> str:
@@ -607,7 +611,9 @@ def save_data(self, data: DATAFRAME_TYPE | pl.LazyFrame) -> dict[str, Any]:
             data = data.collect()
 
         data.write_ndjson(self.file)
-        return utils.get_file_and_dataframe_metadata(self.file, data)
+        if isinstance(self.file, (str, Path)):
+            return utils.get_file_and_dataframe_metadata(self.file, data)
+        return utils.get_dataframe_metadata(data)
 
     @classmethod
     def name(cls) -> str:
diff --git a/tests/plugins/test_polars_extensions.py b/tests/plugins/test_polars_extensions.py
index 2709dd85c..967571141 100644
--- a/tests/plugins/test_polars_extensions.py
+++ b/tests/plugins/test_polars_extensions.py
@@ -147,6 +147,24 @@ def test_polars_ndjson(df: pl.DataFrame, tmp_path: pathlib.Path) -> None:
     polars.testing.assert_frame_equal(df, df2)
 
 
+@pytest.mark.parametrize(
+    ("writer_cls", "reader_cls"),
+    [(PolarsJSONWriter, PolarsJSONReader), (PolarsNDJSONWriter, PolarsNDJSONReader)],
+)
+def test_polars_json_file_objects(df: pl.DataFrame, writer_cls, reader_cls) -> None:
+    buffer = io.BytesIO()
+    write_metadata = writer_cls(file=buffer).save_data(df)
+
+    df2, read_metadata = reader_cls(source=io.BytesIO(buffer.getvalue())).load_data(pl.DataFrame)
+    _, bytes_metadata = reader_cls(source=buffer.getvalue()).load_data(pl.DataFrame)
+
+    polars.testing.assert_frame_equal(df, df2)
+    for metadata in (write_metadata, read_metadata, bytes_metadata):
+        assert "file_metadata" not in metadata
+        assert metadata["dataframe_metadata"]["rows"] == 2
+        assert metadata["dataframe_metadata"]["column_names"] == ["a", "b"]
+
+
 def test_polars_avro(df: pl.DataFrame, tmp_path: pathlib.Path) -> None:
     file = tmp_path / "test.avro"