In order to investigate the effect of saltwater on the ageing of oil mixtures and related tribological performances,the ageing test of lubricating oil containing saltwater (simulated seawater)was carried out in an oven.The physicochemical properties of the lubricating oil during aging process were analyzed,and the effect of the ageing of oil mixtures on roller surface morphology was characterized by optical microscope.The tribological behavior of the aged lubricating oil was studied by ball-on-disc rig,and the chemical analysis of the friction pair surface after the friction test was carried out by using the X-ray electron spectrometer (XPS).The results show that after aging,the viscosity and total acid value of lubricating oil will not change significantly (except ester series oils),however,the wear under the lubrication of the oil mixture with salt water is higher than that of oil mixture without salt water.With the increase of ageing time,the wear under the lubrication of the oil mixture is decreased.This is because of the decrease of oxygen (oxide) concentration on wear scar,which provided less protection to the contacting surface during running in process.