Abstarct: Abstract In this study, 0.15 % weight percent of copper nanoparticles suspension were prepared by different methods in engine oil, and the stability was investigated visually. Then, the selected sample stability was investigated by elemental analysis and dynamic light scattering analysis methods. By an ultrasonic mixer, in the best method the nanoparticles were dispersed in ethanol; then an oleic acid dispersant with a 1: 1 weight ratio of the nanoparticles was added to the ethanol solvent and turned to ultrasonic again. A high-speed centrifuge was used to separate the coated nanoparticles and dry them in an oven. 0.5 % weight percent of the coated nanoparticles were added to the oil and finally combined with the probe ultrasonic for 15 minutes. Then, to test it the pin-on-disk wear was used in two smooth and scratched pin and a quadratic ball wear methods. The stability results proved that the nanoparticles in oil increase the stability by 47% after two months, and also, the suspension nanoparticle stability occurs after 96 days. Wear test results also proved equal average friction coefficient of the baxse and nano oil, in flat surface pin wear, at low temperature and load as high temperature and load, the average coefficient of friction in the presence of baxse oil and nano oil is compared to the non-lubricant state, the coefficient of friction is reduced by 80%. When performing scratch pin wear, the average friction coefficient is equally using the baxse oil and nano oil, at low temperature and load. When using the nano oil at high temperature and load, reduced by 50% compared to the baxse oil. In quadruple ball wear, the average friction coefficient of nano oil has decreased respectively by 0.02 and 0.04 at low and high temperatures compared to the baxse oil. SEM images show that in scratched pin wear, the surface quality improves by nanoparticles when increase the applied load to friction surfaces by filling grooves and repairing surfaces.