diff --git a/homeassistant/components/qnap/sensor.py b/homeassistant/components/qnap/sensor.py
index 7d3ed3ab53e4..75e68b7b1596 100644
--- a/homeassistant/components/qnap/sensor.py
+++ b/homeassistant/components/qnap/sensor.py
@@ -482,7 +482,7 @@ class QNAPVolumeSensor(QNAPSensor):
         if self.entity_description.key == "volume_size_used":
             return used_gb
 
-        if self.entity_description.key == "volume_percentage_used":
+        if self.entity_description.key == "volume_percentage_used" and total_gb != 0:
             return used_gb / total_gb * 100
 
         return None
diff --git a/tests/components/qnap/test_sensor.py b/tests/components/qnap/test_sensor.py
new file mode 100644
index 000000000000..45f47b3316eb
--- /dev/null
+++ b/tests/components/qnap/test_sensor.py
@@ -0,0 +1,48 @@
+"""Test the QNAP sensors."""
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from homeassistant.components.qnap.sensor import _VOLUME_MON_COND, QNAPVolumeSensor
+
+from .conftest import TEST_SERIAL
+
+
+def _make_coordinator(volumes: dict) -> MagicMock:
+    """Create a mock coordinator with the given volumes."""
+    coordinator = MagicMock()
+    coordinator.data = {
+        "system_stats": {
+            "system": {"name": "Test NAS", "model": "TS-1"},
+            "firmware": {"version": "1.0"},
+        },
+        "volumes": volumes,
+    }
+    return coordinator
+
+
+def _volume_sensor(coordinator: MagicMock) -> QNAPVolumeSensor:
+    """Create a volume percentage sensor."""
+    description = next(
+        desc for desc in _VOLUME_MON_COND if desc.key == "volume_percentage_used"
+    )
+    return QNAPVolumeSensor(coordinator, description, TEST_SERIAL, "Volume 1")
+
+
+@pytest.mark.parametrize(
+    ("free_size", "total_size", "expected"),
+    [
+        (75, 100, 25.0),
+        (0, 0, None),
+    ],
+)
+def test_volume_percentage_used(
+    free_size: int, total_size: int, expected: float | None
+) -> None:
+    """Test the volume percentage used sensor."""
+    coordinator = _make_coordinator(
+        {"Volume 1": {"free_size": free_size, "total_size": total_size}}
+    )
+    sensor = _volume_sensor(coordinator)
+    assert sensor.native_value == expected