diff --git a/doc/changes/devel/13251.bugfix.rst b/doc/changes/devel/13251.bugfix.rst
new file mode 100644
index 00000000000..a47faf00f02
--- /dev/null
+++ b/doc/changes/devel/13251.bugfix.rst
@@ -0,0 +1 @@
+Read Nihon Kohden annotation file accurately, by `Tom Ma`_.
diff --git a/mne/io/nihon/nihon.py b/mne/io/nihon/nihon.py
index d6c992dd563..6f3b35018a5 100644
--- a/mne/io/nihon/nihon.py
+++ b/mne/io/nihon/nihon.py
@@ -276,6 +276,45 @@ def _read_nihon_header(fname):
     return header
 
 
+def _read_event_log_block(fid, t_block, version):
+    fid.seek(0x92 + t_block * 20)
+    data = np.fromfile(fid, np.uint32, 1)
+    if data.size == 0 or data[0] == 0:
+        return
+    t_blk_address = data[0]
+
+    fid.seek(t_blk_address + 0x1)
+    data = np.fromfile(fid, "|S16", 1).astype("U16")
+    if data.size == 0 or data[0] != version:
+        return
+
+    fid.seek(t_blk_address + 0x12)
+    data = np.fromfile(fid, np.uint8, 1)
+    if data.size == 0:
+        return
+    n_logs = data[0]
+
+    fid.seek(t_blk_address + 0x14)
+    return np.fromfile(fid, "|S45", n_logs)
+
+
+def _parse_event_log(event_log):
+    t_desc = event_log[:20]
+    hour, minute, second = (
+        int(event_log[20:22]),
+        int(event_log[22:24]),
+        int(event_log[24:26]),
+    )
+    t_onset = hour * 3600 + minute * 60 + second
+    return t_desc, t_onset
+
+
+def _parse_sub_event_log(sub_event_log):
+    t_sub_desc = sub_event_log[:20]
+    t_sub_onset = int(sub_event_log[24:30]) / 1e6
+    return t_sub_desc, t_sub_onset
+
+
 def _read_nihon_annotations(fname):
     fname = _ensure_path(fname)
     log_fname = fname.with_suffix(".LOG")
@@ -292,17 +331,24 @@ def _read_nihon_annotations(fname):
         n_logblocks = np.fromfile(fid, np.uint8, 1)[0]
         all_onsets = []
         all_descriptions = []
+        may_have_sub_blocks = n_logblocks <= 21
         for t_block in range(n_logblocks):
-            fid.seek(0x92 + t_block * 20)
-            t_blk_address = np.fromfile(fid, np.uint32, 1)[0]
-            fid.seek(t_blk_address + 0x12)
-            n_logs = np.fromfile(fid, np.uint8, 1)[0]
-            fid.seek(t_blk_address + 0x14)
-            t_logs = np.fromfile(fid, "|S45", n_logs)
-            for t_log in t_logs:
+            t_logs = _read_event_log_block(fid, t_block, version)
+            t_sub_logs = None
+            if may_have_sub_blocks:
+                t_sub_logs = _read_event_log_block(fid, t_block + 22, version)
+
+            for i, t_log in enumerate(t_logs):
+                t_desc, t_onset = _parse_event_log(t_log)
+                if t_sub_logs is not None and t_sub_logs.size == t_logs.size:
+                    t_sub_desc, t_sub_onset = _parse_sub_event_log(t_sub_logs[i])
+                    t_desc += t_sub_desc
+                    t_onset += t_sub_onset
+
+                t_desc = t_desc.rstrip(b"\x00")
                 for enc in _encodings:
                     try:
-                        t_log = t_log.decode(enc)
+                        t_desc = t_desc.decode(enc)
                     except UnicodeDecodeError:
                         pass
                     else:
@@ -310,9 +356,7 @@ def _read_nihon_annotations(fname):
                 else:
                     warn(f"Could not decode log as one of {_encodings}")
                     continue
-                t_desc = t_log[:20].strip("\x00")
-                t_onset = datetime.strptime(t_log[20:26], "%H%M%S")
-                t_onset = t_onset.hour * 3600 + t_onset.minute * 60 + t_onset.second
+
                 all_onsets.append(t_onset)
                 all_descriptions.append(t_desc)