A lubricating oil composition for diesel engines, particularly a composition with low ashes and no metals. The lubricating oil composition has exceedingly high detergency and excellent antiwear so that it is suitably used for diesel engines equipped with an apparatus for after-treatment of exhaust gas. The lubricating oil composition contains a lubricating base oil which includes a component (A): 2 to 30% by mass, based on the total amount of the composition, of a succinimide compound having an alkenyl group or an alkyl group of a number average molecular weight of 80 to 500 or a boronic compound thereof; and a component (B): 0.5 to 30% by mass, based on the total amount of the composition, of a succinimide compound having an alkenyl group of a number average molecular weight of 800 to 3,500 or a boronic compound thereof.