Abstract: 3 mm thick Q235 steel was friction stir welded using W-Re pin tool at traverse speed of 100 mm/min and tool rotational speed of 450 r/min. The microstructure and mechanical properties of joints were analyzed. The well formed joint without surface defects could be obtained. Tool wear and oxidation occurred after welding. Four distinct zones were identified in the joint cross-section, which experienced different microstructural evolution but all consisted of ferrite and pearlite. The highest microhardness was located in the WNZ. The fracture of joint located at HAZ during tensile test with ductile fracture mode.