Abstract: In order to investigate the corrosion mechanisms of the Cu-Co nanocrystalline bulk alloys as well as the influencing mechanism of the nanocrystallization on its corrosion resistance in H₂SO₄ solution, the corrosion resistance of Cu-50Co nanocrystalline and coarse grained bulk alloys in H₂SO₄ solutions of different concentrations and the effect of the nanocrystallization on them were studied by electrochemical techniques, including the polarization curves, activation energy curves, and electrochemical impedance spectroscopies. It was found that the higher concentration of the solution concentration, the larger corrosion current density of Cu-50Co alloys. When the solution concentration was the same, the corrosion current density of the two Cu-50Co alloys became smaller with the decreased grain size. Moreover, both two Cu-50Co alloys produced passivation phenomena, and the passive current density decreased with the increased solution concentration. Furthermore, the passive current density of the Cu-50Co nanocrystalline alloy was smaller than that of the corresponding coarse-grained alloy. In addition, the electrochemical impedance microscopies of these two Cu-50Co alloys both consisted of single capacitive arc, and the electrochemical reactive resistance and activation energy became smaller with the increased solution concentration. In case of the same solution concentration, the electrochemical reactive resistance and activation energy of the nanocrystalline Cu-50Co alloy are larger than those of the coarse grained one. As a result, the corrosion rate of both samples increases with increased solution concentration, resulting in the decreasing corrosion resistance. For the nanocrustallization Cu-50Co alloy, its corrosion rate reduces and therefore its corrosion resistance is improved.