The casein-acrylonitrile graft copolymer fiber was treated in sodium hydroxide, sodium carbonate, and sodium bicarbonate solutions toevaluate its alkali resistance which was very important for wet processing. The weight loss and whiteness of the treated fibers were examined. UV spectra of the alkaline tratment solutions and IR spectra of the treated fibers were analyzed. The study showed that the fiber exhibited poor alkali resistance. Treating temperature, alkali concentration, and strength affected the weight loss and whiteness of the trated fibers. A high weight loss was found even at low alkali concentration, and the obvious yellowing was observed at higher alakli concentration and temperature. The weight loss was primarily due to hydrolysis of casein, whereas the yellowing was caused by the hydrolysis of nitrile groups and induced formation of C=N conjugation system. (c) 2008 Wiley Periodicals, Inc.