Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from to . The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around , fine particles with a peak around , and coarse particles with a peak around 2 or . Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure.