The effect of Cu content on the corrosion resistance of Zr-1Nb-xCu alloys (x=0~0.5, mass fraction, %) was investigated in superheated steam at 400 ℃ and 10.3 MPa by autoclave tests. The microstructure of the alloys and the fracture surface of oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that when the addition of Cu in the Zr-1Nb alloys is below 0.2%, the main second phase particles (SPPs) are β-Nb in smaller size, and Cu mainly dissolved in the α-Zr matrix, the corrosion resistance of the alloys is improved markedly with the increase of Cu content. When the addition of Cu is above 0.2%, the SPPs of Zr2Cu are precipitated. The size and amount of Zr2Cu particles become larger with the increase of Cu content. The Zr-1Nb-0.35Cu alloy, in which the SPPs of Zr2Cu are moderate in size and amount, shows the best corrosion resistance. However, the Zr-1Nb-0.5Cu alloy, in which the SPPs of Zr2Cu are larger and more, shows the worst corrosion resistance and nodular corrosion appeares during the autoclave tests in superheated steam at 400 ℃.