Abstarct: Numerical and experimental analysis of ratchetting-fatigue interaction was investigated by uniaxial cyclic loading for stress-controlled and strain-controlled tests. The softening and relaxation behavior of specimens were also investigated in this study. Effects of many parameters on fatigue life are studied in this investigation, some of which are: stress or strain amplitude, mean stress or mean strain, stress ratio and number of pre-ratchetting cycles for two steps tests. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. The numerical analysis was carried out by ABAQUS software using three kind of hardening models to describe plasticity: isotropic hardening, linear kinematic hardening and nonlinear isotropic/kinematic hardening and the results were compared with experimental results. Since for SS316 stainless steel specimens peak stress for pure fatigue test is relatively high, overloading influence occurs which resulting in increasing fatigue life. On the other hand, for CK45 specimens the peak stress for pure fatigue test is relatively low and only pre-ratchetting influence occurs which resulting in decreasing fatigue life. In uniaxial cyclic loading for strain-controlled condition, CK45 specimens show different cyclic behavior depend on strain amplitude and number of cycles but SS316 specimens only show softening behavior. For two kinds of specimens by increasing strain amplitude fatigue life decrease greatly. Also, for predicting fatigue life under strain-controlled tests, energy-baxsed models were developed. In general, fatigue life of specimens is greatly depending on mean stress or mean strain and effect of stress amplitude or strain amplitude on fatigue life is very low. The non-linear isotropic/kinematic hardening model simulates the softening and ratcheting behavior of specimens accurately but the isotropic and linear kinematic hardening models can not simulate the softening and ratcheting behavior of specimens.