Cyclic softening behavior of Cr-Mo-V Cast Steel for hot components of steam turbine was evaluated by low cycle fatigue tests. The dependency of the relationship between number of cycles and maximum stress on test conditions was examined. The hardness of interrupted test specimens was related to maximum stress. From these studies, maximum stress during low fatigue test could be estimated by number of cycles and hardness respectively, in terms of strain range. This could make it possible to estimate strain range of low cycle fatigue by number of cycles and hardness of components.