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The effects of polyethylene imine on the corrosion of electroless nickel substrates during immersion gold plating were investigated by XRF, SEM and XPS in combination with open-circuit potential, polarization curves, electrochemical impedance spectrum and infrared (IR) reflection spectrum analysis. The results show that the polyethylene imine decreases the initial deposition rate while it has little effect on the longer deposition rate. The polyethylene imine decreases the concentrations of Ni and O in the gold coating. Moreover, it is also revealed that this additive could be adsorbed on the nickel or gold surface, and the adsorption on gold surface is stronger than that on nickel. The polyethylene imine improves the dissolution of the passivating film which is formed on the surface of the substrate and reduces the difference between activity/passivity of adjacent features of the surface. As a result, in the presence of this agent, the localized dissolution of nickel will be reduced and nickel contained in the substrate composition will be dissolved almost uniformly.