Abstract: A lubricating oil composition comprising a base oil and, incorporated therein, a phosphoric acid ester, phosphorous acid ester, phosphoric acid ester amine salt or phosphorous acid ester amine salt, an aliphatic dicarboxylic acid compound, and an alkylamine compound and/or primary zinc thiophosphate, succinimide or perbasic magnesium or calcium sulfonate. The change with the lapse of time of the friction coefficient of this lubricating oil composition is small and the friction coefficient is stable, and the change of the friction coefficient by the change of the oil temperature is small. By dint of such excellent characteristics, this lubricating oil composition is especially valuable as a lubricating oil for an automatic transmission of an automobile.