Non-degradable metals such as stainless steel, cobalt-chromium-based alloys, titanium and its alloys may lead to stress shielding effect after fractured bone has healed. This complication may attribute to the non-degradability and the mismatch of the mechanical properties between these metallic implants and human bone. Biodegradable metallic materials have been therefore studied as alternative implantable metals in orthopaedics for some years. Magnesium is a potential candidate, as its mechanical properties are similar to human. Additionally, it is degradable and its ions are essential for cell functions. However, rapid degradation and release of hydrogen gas may inhibit its applications clinically. Hence, this paper reviews the development of the biodegradable metallic implants and various methods to improve the degradation of magnesium alloys.