An internal-combustion engine oil composition prepared by adding (a) a boron-containing ashless dispersant, (b) a metallic detergent and, if necessary, (c) at least one member selected from among esters of hydroxylated aromatic carboxylic acids with hydroxy compounds and boron-containing derivatives of the esters to a lube base oil at a [B]/[M] ratio of 0.15 or above {wherein B is the boron content (wt.%) of the composition, and M is the total content (wt.%) of the metals resulting from the metallic detergent in the compostion} and having a sulfated ash content of 1.5 wt.% or below. This composition has a lowered ash content, does not impair the performance of an exhaust posttreatment apparatus and is excellent in coking resistance and oxidation stability.