Abstract: Sa mples of glass fiber (S2 )-epoxy (JF-43) composite prepreg were exposed to 45℃,25℃,5℃ respectively and about 50 percent relative humidity for different periods up to 196 days.They were analyzed in depth using infrared spectroscopy (IR) and other chemical analysis in order to determine the extent of the chemical changes occurring and to study the relationship between chemical changes and temperatures of aging.All showed evidence of significant changes.The temperature of aging had a significant effect on prepreg chemical changes such as epoxy group content,insoluble content and so on.The same samples,which were exposed to 25℃ and about 50 percent relative humidity for different periods up to 77 days, were determined using IR and mechanical property instrument.A linear relationship could be discerned between epoxy group content and laminate mechanical properties such as flexural properties and tensile properties at a confidence level of 99 percent by linear regression to the data.The cured degree calculated from the epoxy index of prepreg would be used as a parameter of quality control.The quality index concerning the importance of monitoring the aging by physicochemical methods was discussed.