Abstract: Friction stir welding process of 5 mm T2 copper was studied. Influence of welding parameters on surface formation of welds,macroscopic appearance of joints,microstructures and mechanical properties were analyzed. The results showed that welded joints without internal defects could be obtained within a wide range of welding parameters. Macroscopic appearance showed that joints consisted of nugget zone,thermo-mechanically affected zone,heat affected zone and parent metal. With increase of rotation speed of the stirring head or decrease of welding speed,bowl-shaped macroscopic appearance of joints got blurred,grains of nugget zone became roughened,and tensile strength of joints was gradually reduced. When welding parameters were 400 r/min,200 mm/min,tensile strength of joints was the highest,reaching 95. 9% of base metal,and S line had no effect on tensile properties of joints. The lowest microhardness occurred in heat affect zone,which was in line with fracture positions of joints.