The effects of three different pretreatments on direct electroless nickel plating of magnesium alloys have been studied by several methods and techniques in order to obtain an environmentally friendly process of pretreatment. The reason of different pretreatments lead to different deposition rates on magnesium alloy was clarified by open circuit potential-time curves. The surface morphology, chemical composition and structure of these coatings were characterized using SEM, EDX and XRD. The results show that all of these nickel coatings have high P content (about 11%), similar surface morphology and structure. Polarization curves show that the corrosion resistance of the coating obtained by H3PO4+HNO3 pickling, K4P2O7 and NH4HF2 activation, respectively, was slightly stronger than the traditional chromic acid methods. The mechanical occlusive force between the coatings and the substrates was increased result from the etched deep cavities by the new pretreatment. Thus, the adherence between the coating and the substrate was improved ultimately.