The optical intrinsic signal imaging (OISI) at 550nm was applied to examine the parietal cortex of focal cerebral ischemia rats with the left middle cerebral artery occlusion (MCAO). A series of spontaneous spreading depression (SD) waves (10.3±4.6 times) were observed during the next 4 h after MCAO. In the earlier 2 h, the SD waves usually spread across the whole left parietal cortex, however, the optical signals showed significant regional differences. During the later 2 h, the waves were restricted in the medial parietal cortex, and the propagated area decreased reversely with the increasing times of SD waves. The baseline intensity in the lateral area increased steadily, up to (8.4±1.2) % at the end of 4 h. By TTC staining, the lateral area proved to infract focus. The results suggested that the optical imaging supplied an effective method to identify the ischemic penumbra and monitor its dynamic evolution.