The corrosion behaviour of AZ91D and NZ30K (Mg-3Nd-0.2Zn-0.4Zr) alloys was investigated in 5% NaCl solution by immersion tests and electrochemical measurements. The immersion tests showed that the corrosion rate of NZ30K was about half that of AZ91D. The localized corrosion of AZ91D was more severe than that of NZ30K due to the higher cathode-to-anode area ratio and higher difference in potential of the cathode phase and the anode matrix. The corrosion of AZ91D concentrated on certain areas and resulted in much deeper corrosion pits, whilst that of NZ30K spread across the surface and led to more uniform and shallow corroded areas. The corrosion products of NZ30K were more compact than those of AZ91D as indicated by SEM. The cyclic polarization curves showed that NZ30K had higher pitting corrosion resistance than AZ91D.