Friction stir processing (FSP) is a new solid state processing technique for microstructure modification and making surface composite in metallic materials. Since this process is done in solid state, the problems caused by freezing and thawing dos not exist. Friction stir processing refines surface microstructure and increases wear resistance by homogenizing surface microstructure and decreasing surface porosity. In this research friction stir processing was succesfully applied to AISI 1045 carbon steel at a tool rotation of 1400 rpm and travel speed of 16, 40 63 mm/min. the microstructure of the samples was analyzed using optical microscopy(OM) and to evaluate the effect of FSP on the tribological behavior of this steel, Pin-on-Disk wear test was performed on the base metal and FSPed samples. The result shows that this process leads to a homogeneous and fine grain microstructure. Also a significant improvement in the wear wear behavior was achieved. In addition, it was found that the wear mechanismof BM and FSPed samples was Adhesive-Delamination mechanism and abrasive mechanism. Moreover, FSP result in increasing of surface hardening. Keywords: Friction Stir Processing, Microstructure, Wear resistance, Surface hardening, AISI 1045 carbon steel