Magnesium alloys are the optimum shell materials for electronic products. These electronic products inevitably contact with the hands of users, and then are corroded by the sweat solution mainly consisting of 0.1 % urea, 0.5% NaCl and 0.5% lactic acid. Electroless plating Ni-P coatings can provide protection to the magnesium alloys shell. The corrosion behaviors of Ni-P coatings deposited on AZ91D magnesium alloys in artificial sweat solution were investigated by electrochemical tests and SEM observations. The results indicated that urea acted as corrosion inhibitor. The inhibiting effect of urea was reduced in NaCl solution or lactic acid solution. NaCl and lactic acid were the main corrosive mediums, and their synergistic effect can significantly accelerate the corrosion of Ni-P coatings. (C) 2007 Elsevier Ltd. All rights reserved.