The invention provides a grease composition for a ball joint which has a low friction coefficient under a load from normal temperatures to high temperatures, a small difference between static friction and dynamic friction, and little change in the friction coefficient even after repeated operation. TO this end, the invention provides a grease composition for a ball joint comprising: (i) a polyisoprene rubber and/or (ii) a polyisoprene rubber viscous material; a specific aliphatic amide and/or a specific aliphatic bisamide; and a specific urea compound.