Diacetate filaments were heat-treated (without tension or with tension) under dry-heat or wet-heat environment, respectively. The effects of temperature, time, and tension on tensile properties of diacetate fibers after heat treatments were discussed. The results show that diacetate fibers present no obvious improvement on its tensile properties after dry-heat treatments without tension. It was also found that during dry heat treatments with tension, the increase in tensile properties of fibers mainly depends on temperature and tension. Moreover, being dry-heat treated with tension instant after wet-heat treatment without tension, diacetate fibers exhibit a higher improvement on its tensile properties comparing with dry heat method with tension. The shrinking measurement for the fibers indicates different supermolecular structures were developed in the fiber before treatment and after treatment, which leads to the different extent in the improvement of tensile properties for the fibers. (c) 2006 Wiley Periodicals, Inc.