Abstract: Objective The purpose was to study effect of welding parameters on friction stir process of A356/6061 dissimilar aluminum alloy. Methods In the paper, experimental research on friction stir welding process of 5 mm thick A356/6061 dissimilar aluminum alloy was conducted to analyze effect of rotational speed and welding speed on microstructure and properties of welded joints. Results The research results showed that when rotational speed was within the range of 1 000～1 150 r/min, incomplete penetration defects appeared on the cross sections of welded joints. As rotational speed increased, degree of defects first decreased and then increased, while tensile strength, yield strength and elongation first increased and then decreased. When welding speed was within the range of 150～200 mm/min, incomplete penetration defects also appeared on the cross sections of welded joints. As welding speed increased, degree of defects gradually increased, tensile strength first decreased and then increased, but overall showing a decreasing state, yield strength first slightly decreased and then increased, elongation gradually decreased. Rotational speed and welding speed affected Mg₂Si reinforcement phase observed in the metallographic microstructure, resulting in its uneven distribution. Conclusion Welding parameters would have effect on reinforcement phase of weld’s microstructure, weld’s root defects and mechanical properties of welded joints.