An experimental model of cerebral infarction in rat brain was successfully established by means of the unilateral internal carotid injection of carbon microspheres. A histopathological investigation of the infarcted brain was performed. The results were as follow: 1. No cerebral infarction was made by the unilateral internal carotid ligation alone. 2. Focal cerebral edema was most marked at the white matter of the embolized hemisphere. 3. The edema was also conspicuous in the deep cerebral gray matter, especially in hippocampus. Degeneration and pyknosis of the neurons were observed at the same area. 4. Transudative hemorrhage in the focal cerebral edema was usually observed in the thalamus. 5. Edematous change in the cortical gray matter was not so marked as compared with the hippocampus and thalamus. 6. Carbon microsphere was not found in the capillaries of ipsilateral choroid plexus. The present experimental model of cerebral infarction will be useful in elucidating the pathological mechanisms of the cerebral infarction.