Cu-30Ni-xRE(x=0-0.213 wt.%) alloy was prepared by adding rare earths (RE) in melted Cu-30Ni alloy using metal mould casting method. The effects of RE on corrosion resistance of the alloy in simulated seawater were investigated using optical microscope, scanning electronic microscope with energy-dispersive spectrometer and electrochemical measurement system. The results showed that the corrosion resistance of Cu-30Ni alloy was greatly improved by adding proper amount of RE, whereas excess addition of RE worsened the corrosion resistance. The optimum RE content was about 0.095 wt.%. In comparison with the alloy without RE, the corrosion potential and corrosion current density of Cu-30Ni alloy containing proper RE decreased by about-40 mV and 0.47 μA/cm~2, respectively. The roles of RE purifying the impurities and decreasing Ni element segregation, which resulted in the decrease of galvanic cell and corrosion potential gradient in Cu-30Ni alloy, were responsible for the improvement of corrosion resistance.