During running-in, the friction coefficient and roughness profile of contacting elements experience changes as a result of asperities deformation and wear. Thus, the operating conditions of running-in period play an important role in the steady-state performance of mechanical elements such as gears, cam-followers, bearings, etc. This project has two separate phases. In phase I an experimental study on the effect of operating conditions of the running-in period on the properties of a tribosystem in the presence of lubricant is conducted. The experiments are conducted using a pin-on-disk test rig and the disk is made of ST37 steel. The selected variables are load, speed, and surface roughness and properties such as running-in length, friction coefficient changes, and weight loss are measured as the outputs. Then using the least-square method and neural network, separate curve fits are developed to relate these parameters to load, speed, and surface roughness. In this paper several experiments have been conducted to investigate the effects of running-in operating conditions such as load, speed, and surface roughness on the duration of running-in, weight loss, and steady-state friction coefficient. The experiments are conducted using a pin-on-disk test rig in the presence of lubricant under the mixed lubrication regime. A number of curve fits are developed based on the experimental data. These curve fits relate the running-in duration, weight loss, initial slope of friction-distance curve, and the steady-state friction coefficient to the running-in operating conditions. It is shown that the higher the running-in speed, the greater the protecting film and the smaller the weight loss. Also, the running-in will last longer. Increasing the applied load results in more asperity-asperity contacts and hence the weight loss increases.It is shown that under constant speed and roughness, increasing the applied load by two folds results in the decrease of the running-in length by about 13%. Doubling the speed with keeping the load and roughness constant results in 19% decrease in the running-in length. The contact of the pin and the disk in the presence of lubricant is modeled using Matlab software and the results are compared to experimental data. In phase II CuO and ZnO nanoparticles are added to the lubricant with the objective of reducing wear quantity in Running-in period. The results indicate that by using nanolubricant with 1% wt zinc oxide and 0.5% copper oxide, the friction coefficient and weight loss reduce more than23% and 60%, respectively. Key words: Wear, Running-in, Pin-on-disk, Least square method, Modeling, Nanolubricant