The solid particles of Fe,Cu,Al,Pb and SiO2 was selected as the contaminants in the engine oils,the effect on the tribological performances of the engine oils by the contaminants content and grain size was studied on the simulated sliding reciprocating motion test rig of the engine piston ring/cylinder liner during boundary lubrication regime.The results show that the presence of the solid contaminants in engine oils leads to an increase in friction coefficient,wear and frictional power losses,increasing the surfaces roughness as a consequence.The friction coefficient,wear and friction power losses are increased with the increasing of contaminants content and grain size.Iron and copper contaminants come first and second in ranking respectively,and this is followed by lead.The presence of the solid contaminants in engine oils impacts negatively on the performances of engine and increases fuel consumption,in order to minimize the effect of solid contaminants,it is necessary to improve the filtration accuracy for engine oils.