The microstructure and corrosion behaviour of hot-rolled Mg-3Zn-1Y-xCu alloys (x=0, 1, 3, 5, wt%) were investigated. Results show that all Mg-3Zn-1Y-xCu alloys mainly consist of α-Mg matrix and Mg₃Zn₆Y phases. The addition of Cu element promotes the formation of MgZnCu phase, and the amount of MgZnCu phase is increased with the increase in Cu content. Electrochemical and immersion test results show that the corrosion resistance of Mg-3Zn-1Y-xCu alloys is deteriorated after Cu addition, which can be attributed to the influence of the microstructure of alloys and the properties of the formed corrosion product film. The MgZnCu phase with high electrochemical potential accelerates the micro-galvanic corrosion as strong cathodic sites, and the decreased protection effect of the corrosion product ?lm results from the variation in PBR value of the related compounds.