diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f45ea8b..c25dc0bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ### New Checks
 
+* Added `check_spatial_series_unit` to validate that SpatialSeries objects (outside of CompassDirection) have a recognized unit string from a curated allowlist of SI length units, angular units, and pixels. [#685](https://github.com/NeurodataWithoutBorders/nwbinspector/pull/685)
 * Added `check_imaging_plane_location_allen_ccf`, `check_electrodes_location_allen_ccf`, and `check_intracellular_electrode_location_allen_ccf` to validate location fields against Allen Mouse Brain CCF ontology terms when subject species is mouse. [#671](https://github.com/NeurodataWithoutBorders/nwbinspector/pull/671)
 * Added `check_time_intervals_start_time_not_constant` to flag TimeIntervals tables where all start_time values are identical, indicating times were likely not set relative to session start. [#677](https://github.com/NeurodataWithoutBorders/nwbinspector/issues/677)
 * Added `check_units_resolution_is_set` to flag when the Units table has spike_times but resolution is not set to a meaningful positive float. [#686](https://github.com/NeurodataWithoutBorders/nwbinspector/pull/686)
diff --git a/docs/best_practices/behavior.rst b/docs/best_practices/behavior.rst
index df68e696..b422d547 100644
--- a/docs/best_practices/behavior.rst
+++ b/docs/best_practices/behavior.rst
@@ -28,6 +28,19 @@ When a :ref:`nwb-schema:sec-SpatialSeries` is in a :ref:`nwb-schema:sec-CompassD
 Check function: :py:meth:`~nwbinspector.checks._behavior.check_compass_direction_unit`
 
 
+.. _best_practice_spatial_series_general_units:
+
+SpatialSeries General Units
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A :ref:`nwb-schema:sec-SpatialSeries` that is not inside a :ref:`nwb-schema:sec-CompassDirection` should have a unit from
+the following recognized set: "meters", "centimeters", "millimeters", "micrometers", "degrees", "radians", "pixels",
+or "n.a." (not available) as a placeholder when the unit is not known.
+These follow the PyNWB convention of full SI words in plural form.
+
+Check function: :py:meth:`~nwbinspector.checks._behavior.check_spatial_series_unit`
+
+
 .. _best_practice_spatial_series_values:
 
 SpatialSeries Data Values
diff --git a/src/nwbinspector/checks/__init__.py b/src/nwbinspector/checks/__init__.py
index 97eee2f2..c01ad2ab 100644
--- a/src/nwbinspector/checks/__init__.py
+++ b/src/nwbinspector/checks/__init__.py
@@ -3,6 +3,7 @@
     check_spatial_series_degrees_magnitude,
     check_spatial_series_dims,
     check_spatial_series_radians_magnitude,
+    check_spatial_series_unit,
 )
 from ._ecephys import (
     check_ascending_spike_times,
@@ -183,6 +184,7 @@
     "check_spatial_series_radians_magnitude",
     "check_spatial_series_dims",
     "check_spatial_series_degrees_magnitude",
+    "check_spatial_series_unit",
     "check_ascending_spike_times",
     "check_electrical_series_unscaled_data",
     "check_units_resolution_is_valid",
diff --git a/src/nwbinspector/checks/_behavior.py b/src/nwbinspector/checks/_behavior.py
index bca5af86..cb8ee3a2 100644
--- a/src/nwbinspector/checks/_behavior.py
+++ b/src/nwbinspector/checks/_behavior.py
@@ -76,3 +76,37 @@ def check_spatial_series_degrees_magnitude(
             )
 
     return None
+
+
+VALID_SPATIAL_SERIES_UNITS = {
+    "meters",
+    "centimeters",
+    "millimeters",
+    "micrometers",
+    "degrees",
+    "radians",
+    "pixels",
+    "n.a.",
+}
+
+
+@register_check(importance=Importance.BEST_PRACTICE_VIOLATION, neurodata_type=SpatialSeries)
+def check_spatial_series_unit(spatial_series: SpatialSeries) -> Optional[InspectorMessage]:
+    """
+    Check that SpatialSeries.unit is a recognized spatial unit.
+
+    Best Practice: :ref:`best_practice_spatial_series_general_units`
+    """
+    if spatial_series.get_ancestor("CompassDirection") is not None:
+        return None
+
+    if spatial_series.unit not in VALID_SPATIAL_SERIES_UNITS:
+        return InspectorMessage(
+            message=(
+                f"SpatialSeries unit '{spatial_series.unit}' is not a valid spatial unit. "
+                f"Valid units are: {', '.join(sorted(VALID_SPATIAL_SERIES_UNITS))}. "
+                "If the unit is not known, use 'n.a.' (not available) as a placeholder."
+            )
+        )
+
+    return None
diff --git a/tests/unit_tests/test_behavior.py b/tests/unit_tests/test_behavior.py
index ee40e619..dd2154b2 100644
--- a/tests/unit_tests/test_behavior.py
+++ b/tests/unit_tests/test_behavior.py
@@ -7,6 +7,7 @@
     check_spatial_series_degrees_magnitude,
     check_spatial_series_dims,
     check_spatial_series_radians_magnitude,
+    check_spatial_series_unit,
 )
 
 
@@ -149,3 +150,68 @@ def test_check_spatial_series_radians_magnitude():
         location="/",
         object_type="SpatialSeries",
     )
+
+
+def test_pass_check_spatial_series_unit():
+    for unit in ("meters", "centimeters", "millimeters", "micrometers", "degrees", "radians", "pixels", "n.a."):
+        spatial_series = SpatialSeries(
+            name="SpatialSeries",
+            description="description",
+            data=np.ones((10,)),
+            rate=3.0,
+            reference_frame="reference_frame",
+            unit=unit,
+        )
+        assert check_spatial_series_unit(spatial_series) is None
+
+
+def test_skip_check_spatial_series_unit_in_compass_direction():
+    compass_direction = CompassDirection(
+        spatial_series=SpatialSeries(
+            name="SpatialSeries",
+            description="description",
+            data=np.ones((10,)),
+            rate=3.0,
+            reference_frame="reference_frame",
+            unit="kilometers",
+        )
+    )
+    spatial_series = compass_direction.spatial_series["SpatialSeries"]
+    assert check_spatial_series_unit(spatial_series) is None
+
+
+def test_fail_check_spatial_series_unit():
+    spatial_series = SpatialSeries(
+        name="SpatialSeries",
+        description="description",
+        data=np.ones((10,)),
+        rate=3.0,
+        reference_frame="reference_frame",
+        unit="kilometers",
+    )
+    result = check_spatial_series_unit(spatial_series)
+    assert result == InspectorMessage(
+        message=(
+            "SpatialSeries unit 'kilometers' is not a valid spatial unit. "
+            "Valid units are: centimeters, degrees, meters, micrometers, millimeters, n.a., pixels, radians. "
+            "If the unit is not known, use 'n.a.' (not available) as a placeholder."
+        ),
+        importance=Importance.BEST_PRACTICE_VIOLATION,
+        check_function_name="check_spatial_series_unit",
+        object_type="SpatialSeries",
+        object_name="SpatialSeries",
+        location="/",
+    )
+
+
+def test_fail_check_spatial_series_unit_none():
+    spatial_series = SpatialSeries(
+        name="SpatialSeries",
+        description="description",
+        data=np.ones((10,)),
+        rate=3.0,
+        reference_frame="reference_frame",
+    )
+    spatial_series.fields["unit"] = None
+    result = check_spatial_series_unit(spatial_series)
+    assert result is not None