It is known that the handle of polyester fiber is improved by the loss of weight, when treated with alkalis. In this study, the effects of alkalis, solvents and accelerating agent on the weight loss of polyester fiber were investigated. When polyester fiber was treated with various alkalis, the weight loss was decreased in the order of KOH＞NaOH＞Na$_2$CO$_3$. With the increase of alkali concentration, temperature and treating time the weight loss was found to be increased. The weight loss was remarkably increased in alcoholic KOH rather than in aqueous KOH solution, and was decreased in the order of ethanol＞propanol＞butanol. The effect of the addition of accelerating agent on the weight loss was remarkable at high concentration, but that of accelerating agent on the weight loss was diminished at low concentration. Drape stiffness, flex stiffness and tearing strength was decreased with increasing the weight loss.