A lubricating oil composition provides enhanced anti-wear and anti-seizure properties, even though reduced in viscosity, suitable for use as an automatic transmission oil, particularly as a metal belt continuously variable transmission oil. The lubricating oil composition contains a base oil and the following based on the total mass of the composition: (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis, (B) a metallic detergent having a total base number of at least 200 mgKOH/g in an amount of 100 to 1200 ppm by mass on a metal basis, and (C) a friction modifier in an amount of 0.01 to 5 percent by mass. The ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to 4.