The butt joints of 6061-T6 /AZ31B with a thickness of 3 mm were obtained using laser welding with a high laser power and welding speed. The macro-morphology, microstructure and fracture feature of the joints were analyzed by the stereo microscope, scanning electron microscope (SEM). The composition of microstructure and fracture surface was analyzed by Energy Dispersive Spectrometer (EDS). The microhardness and tensile strength of the joint were tested. The results showed that the content of intermetallic compound was different in different weld region. There was a large amount of intermetallic compounds Al₁₂Mg₁₇ in the weld zone and fusion zone near AZ31B side. The other areas were mostly the mixed structure of α(Al) and Al₂Mg₃. The presence of intermetallic compounds leaded to the higher hardness of the weld compared to the base metal. The hardness fluctuated in value because of the different intermetallic compounds and their various contents. The tensile strength of 6061-T6/AZ31B dissimilar butt joints by laser welding was up to 34 MPa. It was found that the fracture always occurred in weld zone near AZ31B side, and the fracture mode was typical brittle fracture.