By the means of DSC and SEM, the nickel salt activation process for electroless nickel plating on MAO ceramic layer of magnesium alloy was studied, the activation effect of nickel salt was compared with that of palladium salt. The results show that, nickel salt is practicable to activation of MAO ceramic layer before electroless nickel plating. The activation process includes impregnation in the activator at room temperature and thermal reduction two steps, the activator formula and the thermal reduction process are two important influence factors to activation effect. Comparing the activation effect of nickel salt with palladium salt, the deposition rate of electroless is lower and ultimate thickness of plating layer is thinner, however, the stability of plating solution is better during the plating.