Abstract: A lubricating oil composition is provided, which can reduce friction even when the viscosity is lowered. A lubricating oil composition comprising a lubricating base oil, (A) a cleaning agent containing magnesium, and (B) a zinc dialkyl dithiophosphate, wherein the amount of component (A) is 200 to 1200 ppm by weight of magnesium per total weight of lubricating oil composition; the amount of component (B) is 300 to 1000 ppm by weight phosphorus based on total weight of lubricating oil composition; wherein component (B) comprises (B-1) a zinc dialkyl dithiophosphate having a primary alkyl group, and the proportion of the weight of component (B-1) to the total weight of component (B) is 30 weight % or more; and the concentration of boron [B] is less than 100 ppm by weight.