Grease composition

A grease composition, which comprises a base oil selected from at least one of synthetic hydrocarbon oil, ester-based synthetic oil, and ether-based synthetic oil; a thickening agent selected from at least one of lithium-based soap, lithium-based complex soap, and a urea-based compound; polytetrafluoroethylene resin powders having a number average molecular weight Mn of 20,000-100,000; and zinc dialkyldithiophosphate having straight or branched alkyl groups of at least 3 carbon atoms, preferably 5-13 carbon atoms, and more preferably 8-12 carbon atoms, has not only a distinguished lubricability, when applied to plastic members, but also a distinguished durability as given by change in friction coefficient and wear loss, after the sliding test.