The preparation of responsive fibers from acrylic fibers is studied. Various responsive fibers, such as fibers which change their color on exposure to light or with change in temperature, have been developed and are used commercially However, the responsive material in these fibers are not the fiber itself but chemicals in microcapsules attached to the fibers by finishing, and few fibers exhibit responsive properties by itself. The partial hydrolysis of polyacrylonitrile fibers to obtain pH responsive fibers is presented in this paper. Partial hydrolysis was effected by control of the concentration of the sodium hydroxide used in the hydrolysis, hydrolysis temperature and time. The degree of hydrolysis was evaluated by nitrogen content of the hydrolyzed fibers and their response, change in length, to aqueous solutions of varying pH was studied by continually changing the pH. Significant changes in lengths with pH were observed and the gel transition behavior varied with the conditions of hydrolysis. The hysteresis of the length change was also studied to evaluate the possibilities of using hydrolyzed acrylic fibers as pH sensors.