In order to study the effect of nickel ion implantation on aqueous corrosion behavior, samples of Zircaloy-4 were implanted with nickel ions with fluences ranging from 1x10(16) to 5x10(17) ions/cm(2) using a metal vapor vacuum arc source operated at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface of the samples were analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. Transmission electron microscopy was used to examine the microstructure of the nickel-implanted samples. The potentiodynamic polarization measurement was employed to evaluate the aqueous corrosion resistance of Zircaloy-4 in a 0.5 M H2SO4 solution. It was found that significant improvement was achieved in the aqueous corrosion resistance when the fluence is 1x10(16) Ni/cm(2). For fluences greater than 1x10(16) Ni/cm(2), the corrosion resistance of the implanted zirconium decreased compared with that of as-received Zircaloy-4; the higher the fluence, the worse the corrosion resistance. The mechanism of the corrosion behavior of the nickel-implanted Zircaloy-4 is discussed. (C) 2004 The Electrochemical Society.