In order to investigate the effect of artificial small defects on torsional fatigue strength of high strength steel, fatigue tests for a maraging steel (HV≅740) containing a small hole of diameter=100, 200, and 500μm were carried out. Torsional fatigue limit of the maraging steel was determined by the threshold condition of non-propagating cracks emanating either at the edge of hole or the smooth part of the specimens depending on the diameter of hole. The critical diameter of hole (d_c) which does not influence torsional fatigue strength for several materials is between 100μm and 200μm regardless of hardness. Prediction equation for bending fatigue limit (σ_ω) by the √(area) parameter model was extendedly applied to predict torsional fatigue limit (τ_ω) for both smooth and holed specimens. The fatigue limits predicted by these method were in good agreement with the experimental results.