Nanocrystalline Co-Ni-Fe alloys were synthesized by pulsed electrodeposition. The composition, microstructure and surface morphologies were studied by EDS、XRD, TEM and SEM. The effect of Co content and grain sizes on the electrochemical corrosion behaviour of nanocrystalline Co-Ni-Fe deposits in 3.5wt% NaCl solution were investigated using Tafel polarization curves. The results reveal that the grain sizes of the nanocrystalline fcc Co-Ni-Fe alloys descrease with increasing of the content of Co in the coating. The grain sizes of nanocrystalline Co-Ni-Fe alloys increase with increasing of the annealing temperature，showing a strong （111）texture. The corrosion rates of Co-Ni-Fe alloys decrease first and then increase with increasing of the Co content in the coating. The corrosion rates decline gradually with increasing of the annealing temperature. Comparing to the nanocrystalline deposits, the coarse grain deposit exhibits a quite a different corrosion morphologies.