diff --git a/tests/visualization_tests/matplotlib_tests/test_timeline.py b/tests/visualization_tests/matplotlib_tests/test_timeline.py
deleted file mode 100644
index 84abae7a23..0000000000
--- a/tests/visualization_tests/matplotlib_tests/test_timeline.py
+++ /dev/null
@@ -1,23 +0,0 @@
-from __future__ import annotations
-
-from io import BytesIO
-
-import pytest
-
-from optuna.trial import TrialState
-from optuna.visualization.matplotlib._timeline import plot_timeline
-from tests.visualization_tests.test_timeline import _create_study
-
-
-@pytest.mark.parametrize(
-    "trial_states_list",
-    [
-        [],
-        [TrialState.COMPLETE, TrialState.PRUNED, TrialState.FAIL, TrialState.RUNNING],
-        [TrialState.RUNNING, TrialState.FAIL, TrialState.PRUNED, TrialState.COMPLETE],
-    ],
-)
-def test_get_timeline_plot(trial_states_list: list[TrialState]) -> None:
-    study = _create_study(trial_states_list)
-    fig = plot_timeline(study)
-    fig.get_figure().savefig(BytesIO())
diff --git a/tests/visualization_tests/test_timeline.py b/tests/visualization_tests/test_timeline.py
index 43d38bd489..bd339e9725 100644
--- a/tests/visualization_tests/test_timeline.py
+++ b/tests/visualization_tests/test_timeline.py
@@ -4,6 +4,7 @@
 from io import BytesIO
 import time
 from typing import Any
+from typing import Callable
 
 import _pytest.capture
 import pytest
@@ -12,23 +13,33 @@
 from optuna.samplers._base import _CONSTRAINTS_KEY
 from optuna.study.study import Study
 from optuna.trial import TrialState
+from optuna.visualization import plot_timeline as plotly_plot_timeline
 from optuna.visualization._plotly_imports import _imports as plotly_imports
+from optuna.visualization._timeline import _get_timeline_info
+from optuna.visualization.matplotlib import plot_timeline as plt_plot_timeline
+from optuna.visualization.matplotlib._matplotlib_imports import _imports as plt_imports
 
 
 if plotly_imports.is_successful():
     from optuna.visualization._plotly_imports import go
 
-from optuna.visualization._timeline import _get_timeline_info
-from optuna.visualization._timeline import plot_timeline
+if plt_imports.is_successful():
+    from optuna.visualization.matplotlib._matplotlib_imports import plt
+
+
+parametrize_plot_timeline = pytest.mark.parametrize(
+    "plot_timeline",
+    [plotly_plot_timeline, plt_plot_timeline],
+)
 
 
 def _create_study(
-    trial_states_list: list[TrialState],
+    trial_states: list[TrialState],
     trial_sys_attrs: dict[str, Any] | None = None,
 ) -> Study:
     study = optuna.create_study()
-    fmax = float(len(trial_states_list))
-    for i, s in enumerate(trial_states_list):
+    fmax = float(len(trial_states))
+    for i, s in enumerate(trial_states):
         study.add_trial(
             optuna.trial.create_trial(
                 params={"x": float(i)},
@@ -115,26 +126,36 @@ def test_get_timeline_info_negative_elapsed_time(capsys: _pytest.capture.Capture
         assert bar.complete < bar.start
 
 
+@parametrize_plot_timeline
 @pytest.mark.parametrize(
-    "trial_states_list",
+    "trial_states",
     [
         [],
         [TrialState.COMPLETE, TrialState.PRUNED, TrialState.FAIL, TrialState.RUNNING],
         [TrialState.RUNNING, TrialState.FAIL, TrialState.PRUNED, TrialState.COMPLETE],
     ],
 )
-def test_get_timeline_plot(trial_states_list: list[TrialState]) -> None:
-    study = _create_study(trial_states_list)
-    fig = plot_timeline(study)
-    assert type(fig) is go.Figure
-    fig.write_image(BytesIO())
+def test_get_timeline_plot(
+    plot_timeline: Callable[..., Any], trial_states: list[TrialState]
+) -> None:
+    study = _create_study(trial_states)
+    figure = plot_timeline(study)
+
+    if isinstance(figure, go.Figure):
+        figure.write_image(BytesIO())
+    else:
+        plt.savefig(BytesIO())
+        plt.close()
 
 
+@parametrize_plot_timeline
 @pytest.mark.parametrize("waiting_time", [0.0, 1.5])
-def test_get_timeline_plot_with_killed_running_trials(waiting_time: float) -> None:
+def test_get_timeline_plot_with_killed_running_trials(
+    plot_timeline: Callable[..., Any], waiting_time: float
+) -> None:
     def _objective_with_sleep(trial: optuna.Trial) -> float:
         time.sleep(0.1)
-        trial.suggest_float("x", -1, 1)
+        trial.suggest_float("x", -1.0, 1.0)
         return 1.0
 
     study = optuna.create_study()
@@ -148,10 +169,14 @@ def _objective_with_sleep(trial: optuna.Trial) -> float:
     study.optimize(_objective_with_sleep, n_trials=2)
 
     time.sleep(waiting_time)
-    fig = plot_timeline(study)
-    bar_colors = [d["marker"]["color"] for d in fig["data"]]
-    assert "green" in bar_colors, "Running trial, i.e. green color, must be included."
-    bar_length_in_milliseconds = fig["data"][1]["x"][0]
-    # If the waiting time is too long, stop the timeline plots for running trials.
-    assert waiting_time < 1.0 or bar_length_in_milliseconds < waiting_time * 1000
-    fig.write_image(BytesIO())
+    figure = plot_timeline(study)
+
+    if isinstance(figure, go.Figure):
+        bar_colors = [d["marker"]["color"] for d in figure["data"]]
+        assert "green" in bar_colors, "Running trial, i.e. green color, must be included."
+        bar_length_in_milliseconds = figure["data"][1]["x"][0]
+        # If the waiting time is too long, stop the timeline plots for running trials.
+        assert waiting_time < 1.0 or bar_length_in_milliseconds < waiting_time * 1000
+        figure.write_image(BytesIO())
+    else:
+        pytest.skip("Matplotlib test is unimplemented.")