The invention provides a grease composition for a hub unit bearing employing an angular contact ball bearing, containing (a) as a thickener a mixture of diurea compounds represented by formula (I): R1—NHCONH—R2—NHCONH—R1, formula (II): R1—NHCONH—R2—NHCONH—R3, and formula (III): R3—NHCONH—R2—NHCONH—R3 wherein R1 is cyclohexyl group, R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R3 is a straight-chain or branched alkyl group having 12 to 20 carbon atoms, and (R1/(R1+R3))×100=85 to 95 mol %; (b) a base oil; (c) a molybdenum dialkyldithiocarbamate; and (d) a calcium sulfonate. The grease composition of the invention, when used in the hub unit bearing, shows minimum leakage, excellent anti-flaking properties and satisfactory bearing lubrication life.