Provided is a grease composition for a ball joint that can reduce the wear of a ball seat at a slide region and also has excellent compatibility with a dust cover. The grease composition for a ball joint comprises a base oil, a thickener, and an additive. The base oil contains an ethylene-α-olefin copolymer and the kinetic viscosity of the base oil at 40° C. is 2,000 to 6,000 mm2/s. The additive contains a polar wax (e.g., monoamide wax or ester wax).