To provide a lubricating oil composition attaining all of the characteristics such as sludge formation inhibiting property, wear resistance and frictional performance on high level with well balance and excellent in water separation.

The invention relates to the lubricating oil composition comprising at least one base oil selected from mineral oils, fats and oils, synthetic oils, and a thiophosphoric ester and a distributed viscosity index improver. The lubricating oil composition exhibits sufficient wear resistance and frictional performance under high pressure and high temperature while sufficiently keeping water separation, and sufficiently inhibiting sludge formation even when used for a long time.