The shot peening process is frequently utilized in order to induce compressive residual stresses onbelow a surface, which will remarkably improve the bending fatigue strength of a gear tooth. in this study, two kinds of case-hardened steels, namely the carburized and the carbo-nitrided steels were used. First, bending fatigue strength using a notched plate simulating a gear tooth was investigated. As expected, the bending fatigue strengths of two kinds of case-hardened steels are improved by the shot peening process. If the shot peening process is employed in order to improve the bending fatigue strength of a gear tooth, the surface durability of the shot peened surface may be reduced because of degradation of its surface roughness. On the contrary, it is expected that the surface durability may be improved by compressive residual stresses induced by shot peening. To understand these factors, the surface durability of the shot peened or/an barrelled case- hardened steel rollers was investigated using a two roller contact fatigue testing machine.