Magnesium (Mg) alloys, can potentially be used as biodegradable orthopedic implants because of their biodegradability and good mechanical properties. However, a quick degradation rate and low bioactivity have prevented their clinical application. In order to enhance the corrosion resistance and the in vitro bioactivity of Mg alloys, protective composite coatings were prepared on AZ31 magnesium alloy followed by sol–gel sealing treatment under low-pressure conditions. The morphologies, crystalline structure and the composition of the samples were characterized by SEM, XRD, and XPS. Electrochemical corrosion test and the in vitro bioactivity were also studied. The results indicated that the composite coatings not only improved the corrosion resistance, but also enhanced the in vitro bioactivity of AZ31 Mg alloy. Therefore, Mg alloy treated with micro-arc oxidation and sol–gel offers a promising approach for biodegradable bone implants.