Surface of AM50 magnesium alloy was melted using continuous wave CO2 laser. The microstructure and composition of the melted layer were analysed by scanning electron microscope (SEM), energy dispersion spectrum (EDS) and X-ray diffraction (XRD). The corrosion behaviour of the laser-treated and untreated samples were studied in 3.5% (mass fraction) NaCl solution by measuring electrochemical polarization curves and immerging. The microstructure of the melted layer was refined highly, the composition and structure were more uniform, the β-phase was decreased, Al and impurity elements in solid solution were increased. The experimental results show that the corrosion potential of the laser melted sample is about 37 mV higher than that of the as-received sample, while the anodic current density is about one order of magnitude lower and the pitting corrosion develop more slowly. The corrosion resistance of the laser surface melting of AM50 is significantly improved.