In order to research laser welding of dissimilar magnesium alloys NZ30K and AZ31, the microstructure and property of the joint of AZ31 and NZ30K welded with a CO2 laser is analyzed. A sound weld is formed with the laser power of 4~5 kW and the welding speed of 4 m/min. The joint microstructure, the precipitated phase and weld element distribution are analyzed, the hardness and tensile strength of the joint are also measured. The optical microscope (OM) observation shows that the weld metal is a fusion of the two different alloys, which presents an incomplete mixture and the alloys interweave in wave-form with each other. By X-ray diffraction (XRD) analysis, α-Mg, Mg17Al12 and Mg12Nd phases are identified in the joint. The scanning electron microscope (SEM) shows further fine structure and regions of different chemical compositions in the weld. An obvious concentration gradient of alloying elements crossing the joint is observed too. The hardness of the joint is not lower than that of the base metal. The tensile strength of the joint is 169 MPa, which is lower than those of the base metals.