The present study investigated the role of alloy microstructure and surface roughness on wear and fric-tion behavior of leaded and unleaded tin bronzes. Ball-on-disk experiments were carried out under dryconditions with steel balls sliding against bronze disks. Scanning electron microscopy (SEM), energydispersive electron microscopy (EDX), x-ray photoelectron spectroscopy (XPS) and Auger electron spec-troscopy were performed to analyze the sliding tracks and the ball scars. The wear reducing effect oflead was associated to the formation of an oxidized lead rich layer. When no such film formed on the leaded bronze wear was more severe than in case of unleaded bronze. Nevertheless, the presence of lead in the alloy was a necessary but not sufficient condition to obtain a smeared layer and thus a lubricating effect of the leaded alloy. Two mechanistic hypotheses were formulated to explain the formation of the smeared layer.