Abstract: Ultrasonic spot welding of 3003 aluminum alloy to galvanized steel sheets was conducted to join aluminum and steel sheets with high efficiency. Microstructure characteristics of the joint, effects of the welding parameters on the joint properties, as well as temperature rise in the weld were studied. The results show that: (i) it was possible to ultrasonically weld 3003 aluminum alloy and galvanized steel sheets;(ii) zinc coating was extruded irregularly, direct contact of aluminum alloy and steel locally resulted in the formation of FeAl₃ and Fe₂Al₅ phases;(iii) joint strength increased when the welding time increased within a certain range and then decreased due to the welding time induced microstructure evolution, and a maximal fracture load of 673 N was obtained when the welding duration was about 240 ms and welding pressure was 0.4 MPa;(iv) the maximal temperature in the weld was about 390 ℃.