The purpose of this investigation was to improve the rotating bending fatigue strength of press-fitted shaft assemblies by varying the geometry of press-fitted portion. Four groups of 50mm-diam. press-fitted specimens were used. As the result, comparing with the fatigue limit of press-fitted plain shaft, maximum increase of the fatigue limit was obtained for the filletted shaft, in which the press-fitted hub had a low protrusion on the face. Taking the reduction of fretting corrosion into consideration, however, the press-fitting of hub overhanging from the shoulder was most preferable with an increase of fatigue limit about 50%. The fatigue limit of the press-fitted plain shaft could be increased by 50% due to press-fitting of hub which had the low protrusion.