<p>Gear-running tests were first carried out using casecarburized Ni-Mo pre-alloy sintered steal gears with different densities of 7.30 g/cm³, 7.40 g/cm³ and 7.54 g/cm³. The load bearing capacity of P/M gears was increased by 5-15% by gear surface rolling, whose effect was most remarkable for P/M gears with a middle density. The surface fatigue strength after 1.0×10⁷ cycles of surface rolled P/M gears with a density more than 7.40 g/cm³ were higher than that of case-carburized Cr-Mo wrought steel gear. These experimental results were then analytically investigated by examining the contact stress distributions around the operating pitch point of P/M pinion using an original two-dimensional finite element model considering voids. The peak of the maximum shear stress τ_max decreased as the amount of fully surface-densified depth δ increased, and there was only a slight difference in the τ_max distribution for every P/M pinion when δ reached 0.3mm. These simulation results appear to explain the durability test results well and reveal the appropriate δ level.</p>