The in vitro and in vivo degradation behavior of an experimental Mg alloy with high corrosion resistance has been investigated and compared with that of a commercial AZ31 Mg alloy with a similar chemical composition. In vitro tests indicated that the experimental alloy is >2.5 times more resistant to degradation than AZ31 during immersion in HBSS at 37 ℃ for 72 h. In vivo tests in the femoral vein of a mouse confirmed that the former degrades much more slowly and uniformly in the biological environment than the latter. Compared with WE43 and JDBM alloys, which are currently considered promising candidates for Mg-based biodegradable materials, the experimental alloy in this study showed better degradation resistance with a similar level of biocompatibility. Microstructural and electrochemical factors affecting the degradation behavior of the alloys in this study are also discussed.