Poly(ethylene terephthalate) multifilament yarn, textured yarn and staple were treated with potasium hydroxide. Time, temperature and concentration of base were seleeted as va- riables. Degradation of tlıe products was investigated in terms of percentage loss in weight, vis- cosity measurements and percent elongation at break.It was observed that textured yarn has greater loss in weight than either multifilament yarn or staple. However ali products showed the same reduction in viscosity. As a result of tre- atment with base the mechanical s*rength of the textured yarn decreased wilh increasing base concentration and time.