Alkaline hydrolysis behaviors of aminoazobcnzene, disperse dyes containing ortho cyano substituent in acceptor ring were examined and proposed their hydrolysis mechanism. The dye which has ortho cyano substituent in acceptor ring was very easily and vapidly hydrolyzed by alkali and showed both large hypsochromic and hypochromic shifts in NaOH solution. These may be resulted from a decrease of electron-withdrawing ability of acceptor by hydrolysis. Its hydrolyzed produces were water-soluble and undyeable. Molecular weights of the water-soluble products. obtained from moss spectrometer, were around half of that of original dyes. And their alkaline hydrolysis may be caused by the rapid nucleophilic attack of OH on the carbon atom adjacent to auto group.