A chrome-free chemical conversion process using sodium stannate as the main component was investigated for corrosion protection of Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr magnesium alloy (GW93). Corrosion property of the specimens with and without chemical conversion film was evaluated by full immersion test in neutral 3.5wt% NaCl solution. The microstructure and phase composition of the chemical conversion film were analyzed by optical microscope, X-ray diffraction meter and scanning electron microscope. The results show that the optimum chemical conversion processing for GW93 magnesium alloy is Na2SnO3 50 g/L, Na4P2O7 50 g/L, NaOH 5 g/L, CH3COONa 15 g/L, citric acid 3 g/L and sodium carbonate 20 g/L at 80 oC for 15 min. Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr is covered by uniform chemical conversion coating composed of MgSnO3·3H2O. The immersion test shows that the average corrosion rate of the specimen without chemical conversion treatment is 6.1083 g·a-1·cm-2, and that of the specimens with chemical conversion treatment is 0.1264 g·a-1·cm-2. Corrosion resistance is improved by 97.9%, which suggests that stannate chemical conversion treatment could provide effective corrosion protection for GW93 magnesium alloy.