This study performs cyclic stress-strain tests to investigate the effect of age-related degradation on the cyclic properties of nuclear structural materials. Aged CF8A cast austenitic stainless steel (CASS) and 33% cold-worked (CW) TP316L stainless steel (SS) are used for the experiment. Aged CF8A CASS is prepared by accelerated aging at 400oC for 4,292hrs, which is equivalent to the aging at 316oC for 32 effective full power years. CW TP316L SS is a simulated material for irradiation hardening and embrittlement of TP316L SS. From the results of tests, the effects of thermal aging and irradiation hardening on the cyclic hardening, cyclic stress-strain curve, and fatigue life of both materials are investigated.