This is the first report on ultrasonotomography of a megacholecyst in the water buffalo.The area of the megacholecyst sonogram reached 159cm2 and the perimeter 686mm.Its size was six times larger than that of normal cholecysts of buffaloes.The sonogram of the megacholecyst was described and measured,and compared with cholecyst sonograms of 11 buffaloes and 18 cattle.The size of cholecysts in one hundred live cattle undergoing surgical operation and that of 50 fresh specimens obtained from the market were also compared with that of the sonogram of this megacholecyst.