<p>In this study, sintered and powder-forged rollers and gears with different densities and nickel contents were fatigue-tested using a roller testing machine and a gear testing machine in order to elucidate their fatigue strength. These experimental results were compared with the results of ingot steel ones. The hardness near the surface of the test specimens with higher nickel content was smaller than that of the other ones. The pores in the sintered rollers became smaller or were disappeared by the hot forging. The fatigue strength of the sintered rollers and gears was the lowest in this experimental range. The fatigue strength of the powder-forged rollers and gears was roughly equivalent to that of the ingot steel ones. The fatigue strength of the test specimens increased as their density increased, and was hardly influenced by the nickel content in this experimental range. It was clear that the fatigue strength of the sintered and the powder-forged rollers and gears was proportional to the hardness at the failure depth for each nickel content.</p>