A lubricating oil composition of SAE viscosity grade 0W20 which comprises a base oil and additive components comprising a nitrogen-containing ashless dispersant, an alkaline earth metal-containing detergent, a phosphorus-containing wear inhibitor, an oxidation inhibitor and a viscosity index improver and which shows a viscosity index of 200-240, a HTHS viscosity of not less than 2.9 mPa·s s at 150° C. and a Noack evaporation loss of not more than 13% favorably gives a high fuel economy and high wear inhibition to a four cycle gasoline engine of motorcycles and a diesel engine mounted on motor cars equipped with an exhaust gas post-processing apparatus.