Abstract: The excess enthalpy relaxation(EER) process and changes of physical and mechanical properties in a crossly linked unsaturatel polyetes annsaled at temperatures below T_g have been studied.The results suggest that not only the amount of EER as determined from the endothermic peak in T_g interval but also the density,T_g and the real part of Yong's,modulus increase with annealing time,while the imaginary patr of the modulus and the internal fricton decrease.The activation energy of EER proeess determined from the rate of EER as a function of annealing temperature is about 7Keal/mole.The molecular mechanism of EER proeess is discussed.