Abstract: Influence of extrusion deformation on the corrosion rate of pure magnesium was studied by means of weight loss,gas collection and electrochemical methods in 35 g·L-1 NaCl solution.The results show that the dynamic re-crystallization of pure magnesium occurres during the process of the extrusion deformation and the grain size is decreased from the size of a few hundreds micro meter (μm) to 25 μm.The area of grain boundaries as the anode is increased by the deformation.The reaction rate of the anode is much quicker than the magnesium without deformation and the corrosion resistance is decreased.