It is an object of the present invention to provide a grease composition, for an outer ring rotation type rolling bearing, which is capable of satisfying all of high-temperature durability, low-temperature property, peeling resistance, and rust-preventive property. A grease composition (7) to be enclosed in the outer rig rotation type rolling bearing for use in automotive electric auxiliary machines contains base oil, a thickener, a peeling-resistant additive, a wear-resistant additive, and a rust-preventive agent. The base oil is mixed oil of trimellitic acid ester oil and synthetic hydrocarbon oil mixed therewith in a mass ratio of (70:30) to (90:10). The thickener consists of a diurea compound shown by a formula (1). R1—NHCONH—R2—NHCONH—R1  (1) wherein a reference symbol R2 denotes a divalent aromatic hydrocarbon group having a carbon number of 6 to 15, and a reference symbol R1 denotes a cyclohexyl group.