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Fatigue tests were performed on smooth tubular specimens of steels with different deformation properties to investigate the effect of static loadings on torsional fatigue over the life from low to high cycle regions. For deformation-controlled test, the effect of static torque on the lifetime in low cycle regime was negligible due to mean stress relaxation after short number of cycles. For load-controlled test under fully-reversed torsion with static torque or tension in wide range of life, reduction of the fatigue life was revealed in both steels irrespective of the condition of static load. Variation of cyclic stress-strain response and accumulation of ratcheting strain were studied under various condition of static torque or tension. Based on the experimental results, a shear strain-based model including mean stress effect on critical plane was modified taking the influences of variation in cyclic strain and accumulation of ratcheting strain into consideration. The model can explain the influence of static load on torsional fatigue life of the present materials.