There is provided a grease composition, including: a base oil; a metal soap thickener formed of at least one metal selected from the group consisting of lithium, calcium, magnesium and aluminum and a fatty acid containing at least one selected from the group consisting of a hydroxyl group, a carboxyl group and a carboxylic acid metal salt group in each molecular structure; and nanoparticles formed of at least one selected from the group consisting of oxides, carbides and diamond materials.