Abstract: Low-cycle fatigue behavior of 2.25Cr1MoV steel at 455 ℃ were studied by using a MTS 810 fatigue testing system under strain-controlled conditions. The results reveal that the steel exhibited obvious cyclic softening feature. Strain ratio had no influence on cyclic softening feature but resulted in mean tensile stress. The mean stress relaxed to zero in early stage of life with the increase of cycle numbers. Fatigue crack initiation patterns had not changed by strain ratio, and hysteresis loop and fatigue life of the steel were not appreciably affected by the mean strain. The low cycle fatigue life for symmetric cycle was same with that for unsymmetirc cycle.