Saponification kinetics of acrylic terpolymer and polyacrylonitrile were studied. The influence of alkali concentration and the time of hydrolysis on the degree of saponification were determined by the residual nitrogen content. The order of reaction was graphically determined and the rate of saponification was found to be faster in the terpolymer than in the homopolymer. Chemical and infrared spectroscopy methods reveal that the reaction is initiated through cyclization of nitrile groups, followed by hydrolysis to amide and carboxylic groups of the ‒(C˭N)n‒ segments produced.