The microstructure and corrosion behaviour of hot-rolled Mg-3Zn-1Y-xCu alloys (x = 0, 1, 3, 5 wt%) were investigated. All alloys mainly consisted of α-Mg matrix and Mg3Zn6Y particles. The addition of Cu formed MgZnCu phase, and the amount of MgZnCu phase increased with the increasing Cu content. The deteriorated corrosion resistance of Mg-3Zn-1Y-xCu alloys with Cu addition had been proved by the electrochemical and immersion results, which can be attributed to the in?uence of the microstructure of alloys and properties of the formed corrosion products ?lm in the corrosion media. The formed MgZnCu particles with high electrochemical potential as strong cathodic sites accelerate the micro-galvanic corrosion and degraded the protectiveness of the corrosion product ?lm resulting from changed PBR of related compounds.