The present invention provides grease a compositions having excellent properties which comprises base oil consisting of specified amounts of a chain hydrocarbon oligomer and the addition polymerization oligomer of alkylene oxide and polyvalent alcohol and the defined amounts of specific additives, such as lithium salt of higher fatty acid, quaternary ammonium salt-containing clay mineral, polar solvents and the like. The grease composition can be applied effectively, for example, on the plastic parts of automobiles, plastic parts of sound apparatus, sliding contact switches and the like.