Abstract: Laser weldingbrazing of AZ31B Mg alloy to T2 pure copper with filler was carried out in a lap configuration. The influence of heat input on microstructure, the phase structure, microhardness and mechanical properties were investigated. The results indicated that joint with good appearance and strength were obtained using proper welding parameters. The maximum shear strength can be 164.2 MPa, which was 64% of the magnesium alloy. When the heat input was low, the thin Mg-Cu eutectic structure was formed at the Mg/Cu interface, while the structure was varied into αMg+(Mg、Al)2Cu eutectic structure/Mg2Cu+Cu2Mg intermetallic compound/Mg-Al-Cu ternary compound/Mg2Cu+Cu2Mg intermetallic compound from fusion zone to Cu side with the increase of heat input. The variation of hardness value from fusion zone to Cu side increased first followed by sharp decrease, and then went up slowly, with the maximum value of 165 HV. The presence of MgCu intermetallic compound near the interface influenced the joint strength, where fracture occurred.