Based on experimental of irradiation of 60 rabbit's brain with a CO2 laser, we studied the ultrapathologicai change and the reversity of the damaged tissue. The author thought that the damaged area of brain tissues irradiated by CO2 laser could be classified into 4 zones : charring zone, coagulation zone, edema zone and periedema zone. The total width is about 380 μm and the irreversible area of damaged tissue is about 300 μm.