Mg-Dy alloys have shown to be promising for medical applications. In order to investigate the influence of ageing treatment on their mechanical and corrosion properties, three Mg-xDy alloys (x=10, 15, 20. wt%) were prepared. Their microstructure, mechanical and corrosion behavior were investigated. The results indicate that ageing at 250. °C has little influence on the mechanical and corrosion properties. In contrast, ageing at 200. °C significantly increases the yield strength, and reduces the ductility. After ageing at 200. °C, the corrosion rate of Mg-20Dy alloy increases largely in 0.9. wt% NaCl solution, but remains unchanged in cell culture medium.