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Silver based composites with varying concentration of graphite and/or MoS 2 were prepared by powder metallurgy method. Impacts of composition on the tribological performance of the composites in ambient air and vacuum were investigated. The lowest friction in air was achieved by Ag-20G (vol.-%) composite, while Ag-20MoS 2 exhibited the best lubricity in vacuum. XPS evaluation revealed the oxidation of MoS 2 in air and a decrease concentration of graphite on the surface of the wear tracks under vacuum. As the proportion of graphite to MoS 2 increased, the friction coefficient and the wear rates ascended gradually in air while decreased sharply under vacuum. As compared with other compositions, Ag-15MoS 2 -5G exhibited a comparable stable and good tribological performance as the environmental condition changed for its friction coefficient and wear rate remained around 0?14 and 5610 26 mm 3 N 21 m 21 .