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The present work was intended to increase the rolling-contact fatigue life of the crank pin for a motorcycle. The small motorcycle uses a needle roller bearing at the big end of the connecting rod. The needle roller exerts high Hertzian stress on the crank pin. This stress sometimes causes rolling-contact fatigue failure such as pitting. The contaminated oil accelerates the rolling-contact fatigue failure. In order to increase the life of the crank pin, not only the quality of the steel but also the casehardening treatment plays an important role. In the present work, a high quality Cr-Mo steel containing oxygen concentration below 10 ppm was chosen as the base steel. The rolling-contact fatigue life was compared in four types of casehardening: normal carburizing, carbonitriding, super-carburizing and super-carbonitriding. A thrust-type testing machine was used during these comparison tests.