Abstract: Rapeseed oil as an environmental friendly lubricant is becoming widely used. Two kinds of dithiophosphorics acid imidazolium salts were synthesized and the tribological properties were tested as anti-wear additive in rapeseed oil. The results of four-ball tests and the wear scar surface morphology analysis show that both the two additives exhibited excellent anti-wear, friction-reduction properties and good extreme pressure property. The friction coefficient decreased from 0.11 to 0.07, the wear scar diameter decreased from 0.82 mm to 0.28 mm and P_B value increased from 490 N to 981 N. The XPS analysis shows the formation of a protective film on the worn surfaces by physical deposition and chemical reaction. Therefore, the synthesized imidazolium salts were excellent anti-friction and anti-wear additives in rapeseed oil and applicable for practice.