Abstract: Alkaline hydrolysis properties of modified polyester fiber containing soldium-5-sulfo-iso-phthalate(SIP) is studied. Experiments indicate that weight loss of the fiber has good linear relationship with treatment time at constant temperature and lower NaOH concentration, and the degree of fiber weight loss increases with the increase of SIP in the HCDP fiber. Besides treatment temperature, alkaline concentration, and treatment time, weight loss of the fibers is affected by profiled cross-section of fibers considerably. Owing to the different hydrolytic degree between HCDP and PET, after treatment, more microcellular structures on the surface of HCDP, indicating that the fiber has better water transportation ability.