PURPOSE: To provide the subject lubricant composition which has ring wear resistance, liner wear resistance, corrosion-resistance at low temperatures, and adequate viscosity at high temperatures, by adding specific amount of chlorinated borate as ashless dispersant, perbasic metal compound, and polybutene to lubricating oil.

CONSTITUTION: (A) more than 0.1wt.% (preferably 0.5-3wt.%) borated chlorinated borate as ashless dispersant (for preferable example, borated chlorinated polyisobutenyl succinic polyalkylene amine anhydride reaction products whose polyisobutenyl part contains 900-2500 molecules averagely), (B) more than 10wt.% (preferably 12.5-30wt.%) perbasic metal compounds, and (C) more than 0.005wt.% (preferably 0.05-0.5wt.%) polybutene whose weight-average molecular weight is more than 100000 are mixed with main oil which has lubricating viscosity, such that boron content of the mixture is more than 0.001wt.% and TBN is more than 20. This composition is available especially for both of a cross head engine and a trunk piston engine.