Abstract: In this study, we investigated the friction and wear behavior of brass (i.e. 64% copper and 36% Zinc) sliding against 100Cr6 under lubricated conditions on a tribometer based on in-situ holographic microscopy and radionuclide technique. Microstructure evolution of friction surfaces were investigated by in-situ holographic microscopy, and surface of CuZn36 was measured real-time wear with high resolution by radionuclide technique. Worn surfaces of CuZn36 plates and 100Cr6 spheres were observed and analyzed by scanning electron microscopy. X-ray photoelectron spectroscopy depth profiles were obtained from the worn surface of CuZn36. The results indicate that the good runningin behaviors (i.e. lower friction and wear) of CuZn36 sliding against 100Cr6 were obtained with varying contact pressures (1.9~3.0 MPa). It suggests that the wear-resistant layers of ZnO were formed in the near-surface region of the wear surfaces, which had good characteristics of high hardness and self-lubrication. During poor running-in experiments, the wear-resistant layers were repeated forming and damaging in a dynamic process. Fatigue wear was the main behavior during good running-in experiments, and adhesion wear and abrasive wear were the main behaviors during poor running-in experiment.