Abstract: Friction stir butt welding of 5 mm thick Cu-Cr-Zr alloy plate was carried out, and the joint was heat treated at different aging temperatures (400, 450, 500 ℃). The effects of heat treatment on the microstructure and mechanical properties of the joint were analyzed. The results show that after postweld heat treatment, the grain size in the nugget zone did not change significantly, and the bended grains in the thermo-mechanically affected zone basically disappeared. After postweld heat treatment, the strengthened precipitates soluted in the matrix during the welding process re-precipitated; the over-aging of the joint after postweld heat treatment at 500 ℃ occurred. After postweld heat treatment, the hardness and tensile strength of the joint obviously increased. The hardness was distributed in a “W” shape and the lowest hardness appeared in the thermo-mechanically affected zone. The hardness and tensile strength hardness of joint after postweld heat treatment at 450 ℃ were both largest; the hardness of the nugget zone was 83% of the base metal, and the tensile strength of the joint was 270 MPa which increased by 50 MPa compared with that before postweld heat treatment.