An oil composition which is useful as a lubricating oil, a heating medium oil, an oil for heat treatment, an oil for electric discharge machining or the like and which suffers from less oxidative degradation even in an oxidizing atmosphere, said composition comprising (A) 100 parts by weight of a petroleum base oil and/or a synthetic base oil and (B) 0.1 to 20 parts by weight of a fraction having a boiling point ranging from 160 to 550 °C obtained from a hydrogenated pitch produced by hydrogenating a pitch resulting from primary heat treatment of a petroleum heavy oil and/or a coal heavy oil, and/or another fraction having a boiling point ranging from 160 to 550 °C obtained by performing further secondary heat treatment of the above-mentioned hydrogenated pitch.