The anterior chorioidal artery was dissected with electro-cautery in 34 cases of cats, which were classified into 5 groups by the postoperative periods (2, 5, 8, 12, 17 days), the disturbance of the blood supply was investigated. Encephalomalacia did nod occur in all of the supplying area of this vessel, but the most common areas of encephalomalacia were Capsula-interna, Pallidum and Tractus opticus and Lobus piriformis, as stated in the followings. 1. Capsula interna 97.1% 2. Pallidum 44% 3. Anonymous part 70.6% 4. A part of lobus piriformis 76.5% 5. A part of tractus opticus 58.8% 6. A part of cornus ammonis 2.9% 7. A part of thalamus 8.8% 8. A part of radiatio optica 2.9% 9. A part of Nucleus amygdalae 5.9% From this experiment, it would appear that the effective mechanism of occlusion of the anterior chorioidal artery is the lesion of the pyramidal tract at the internal capsule and the destructon of a part of Globus pallidus.