diff --git a/sagemaker-train/src/sagemaker/train/model_trainer.py b/sagemaker-train/src/sagemaker/train/model_trainer.py
index f2eeb6705e..df7b0003ec 100644
--- a/sagemaker-train/src/sagemaker/train/model_trainer.py
+++ b/sagemaker-train/src/sagemaker/train/model_trainer.py
@@ -1391,7 +1391,7 @@ def _prepare_train_script(
             execute_driver=execute_driver,
         )
 
-        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w") as f:
+        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w", newline="\n") as f:
             f.write(train_script)
 
     @classmethod
diff --git a/sagemaker-train/tests/unit/train/test_model_trainer.py b/sagemaker-train/tests/unit/train/test_model_trainer.py
index a002b556b6..ad936461e2 100644
--- a/sagemaker-train/tests/unit/train/test_model_trainer.py
+++ b/sagemaker-train/tests/unit/train/test_model_trainer.py
@@ -1617,6 +1617,93 @@ def mock_upload_data(path, bucket, key_prefix, extra_args=None):
     assert kwargs["tensor_board_output_config"].local_path == "/opt/ml/output/tensorboard"
 
 
+@patch("sagemaker.train.model_trainer.TrainingJob")
+@patch("sagemaker.train.model_trainer.TemporaryDirectory")
+def test_prepare_train_script_uses_lf_line_endings(
+    mock_tmp_dir, mock_training_job, modules_session
+):
+    """Test that _prepare_train_script generates sm_train.sh with LF line endings only."""
+    modules_session.upload_data.return_value = (
+        f"s3://{DEFAULT_BUCKET}/{DEFAULT_BASE_NAME}-job/input/test"
+    )
+
+    tmp_dir = tempfile.TemporaryDirectory()
+    tmp_dir._cleanup = False
+    tmp_dir.cleanup = lambda: None
+    mock_tmp_dir.return_value = tmp_dir
+
+    try:
+        model_trainer = ModelTrainer(
+            sagemaker_session=modules_session,
+            training_image=DEFAULT_IMAGE,
+            source_code=DEFAULT_SOURCE_CODE,
+            role=DEFAULT_ROLE,
+        )
+
+        model_trainer.train()
+
+        train_script_path = os.path.join(tmp_dir.name, TRAIN_SCRIPT)
+        assert os.path.exists(train_script_path)
+
+        with open(train_script_path, "rb") as f:
+            content = f.read()
+
+        # Verify no CRLF line endings exist
+        assert b"\r\n" not in content, "sm_train.sh contains CRLF line endings; expected LF only"
+        # Verify LF line endings are present
+        assert b"\n" in content, "sm_train.sh does not contain any LF line endings"
+    finally:
+        shutil.rmtree(tmp_dir.name, ignore_errors=True)
+
+
+@patch("sagemaker.train.model_trainer.TrainingJob")
+@patch("sagemaker.train.model_trainer.TemporaryDirectory")
+def test_prepare_train_script_opened_with_lf_newline(
+    mock_tmp_dir, mock_training_job, modules_session
+):
+    """Regression for #5897: sm_train.sh must be opened with ``newline="\\n"``.
+
+    On Windows, text-mode ``open(..., "w")`` translates ``\\n`` to ``\\r\\n``, which breaks
+    the bash script inside the Linux training container. Byte-level assertions alone pass
+    on POSIX hosts even without the fix, so this test inspects the ``open`` call itself and
+    therefore holds independently of the test host OS.
+    """
+    modules_session.upload_data.return_value = (
+        f"s3://{DEFAULT_BUCKET}/{DEFAULT_BASE_NAME}-job/input/test"
+    )
+
+    tmp_dir = tempfile.TemporaryDirectory()
+    tmp_dir._cleanup = False
+    tmp_dir.cleanup = lambda: None
+    mock_tmp_dir.return_value = tmp_dir
+
+    train_script_newlines = []
+    real_open = open
+
+    def tracking_open(file, mode="r", *args, **kwargs):
+        if str(file).endswith(TRAIN_SCRIPT) and "w" in mode:
+            train_script_newlines.append(kwargs.get("newline"))
+        return real_open(file, mode, *args, **kwargs)
+
+    try:
+        model_trainer = ModelTrainer(
+            sagemaker_session=modules_session,
+            training_image=DEFAULT_IMAGE,
+            source_code=DEFAULT_SOURCE_CODE,
+            role=DEFAULT_ROLE,
+        )
+
+        with patch("builtins.open", side_effect=tracking_open):
+            model_trainer.train()
+
+        assert train_script_newlines == ["\n"], (
+            "sm_train.sh must be opened with newline='\\n' to keep LF endings, "
+            f"got {train_script_newlines}"
+        )
+    finally:
+        shutil.rmtree(tmp_dir.name, ignore_errors=True)
+
+
 @patch("sagemaker.train.model_trainer.TrainingJob")
 def test_input_merge(mock_training_job, modules_session):
     model_input = InputData(channel_name="model", data_source="s3://bucket/model/model.tar.gz")