The purpose of the present invention is to provide a roller bearing grease composition for outer ring rotation, whereby the characteristics of high-temperature durability, low-temperature properties, peeling resistance, and anti-rust properties can all be satisfied. A grease composition 7 sealed in a roller bearing for outer ring rotation used in auxiliary electric equipment of an automobile is characterized by containing a base oil, a thickener, an anti-peeling additive, an antiwear additive, and a rust inhibitor, the base oil being an oil blend in which the ratio (trimellitic acid ester oil:synthetic hydrocarbon oil) of a trimellitic acid ester oil and a synthetic hydrocarbon oil in terms of mass ratio is 70:30 to 90:10, and the thickener being a diurea compound represented by formula (1). In the formula, R2 represents a C6-15 divalent aromatic hydrocarbon group, and R1 represents a cyclohexyl group.