Magnesium alloys are potential biodegradable implant materials. However, magnesium alloys normally corrode rapidly in the in-vivo fluid, resulting in subcutaneous gas bubbles and alkalisation of the in-vivo solution. The paper presents a new approach to control the degradation rate of magnesium in a simulated body fluid (SBF) through employing a recently developed anodising technique. It was found that the ceramic like anodised coating formed on the surface of magnesium can effectively slow down the biodegradation process and hence result in slow hydrogen evolution and solution alkalisation processes. The results imply that an anodised magnesium alloy may be successfully used as a biodegradable implant material.