The effects of nickel electroplating on electrical properties of PMN-based relaxor ferroelectrics were studied by measuring the resistance and temperature dependence of dielectric constant and dissipation factor. It was found that the insulation resistivity of the specimens declined nonlinearly with electroplating time. Additionally, the dielectric constant and dissipation factor were reduced and enhanced respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that Nb5+ and Pb2+ were partially reduced to Nb4+ and metallic Pb by hydrogen during nickel electroplating, which consequently generated oxygen vacancies and conductive electrons in view of defect chemistry, thereby the conduction was enhanced. On the basis of our experiments, the degradation of electrical properties of PMN-based ferroelectrics was ascribed to resistive leakage resulting from Nb5+ and Pb2+ reductions to lower charge states by hydrogen.