The tribological behavior Of Mo5Si3-particle-reinforeed silicon nitride (Si3N4) composites was investigated by pin-on-plate wear testing under dry conditions. The friction coefficient of the Mo5Si3-Si3N4 composites and Si(3)N4 essentially decreased slowly with the sliding distance, but showed sudden increase for several times during the wear testing. The average friction coefficient of the Si3N4 decreased with the incorporation of submicrometer-sized Mo5Si3 particles and also as the content of Mo5Si3 particles increased. When the Mo5Si3-Si3N4 composites were oxidized at 700degreesC in air, solid-lubricant MoO3 particles were generated on the surface layer. Oxidized Mo5Si3-Si3N4 composites showed self-lubricating behavior, and the average friction coefficient and wear rate of the oxidized 2.8 wt% Mo5Si3-Si3N4 composite were 0.43 and 0.72 x 10(-5) mm(3) (N . m)(-) 1, respectively. Both values were similar to30% lower than those for the Si3N4 tested in an identical manner.