Water jet cavitation peening (WJCP) was used to strengthen the surface of nickel-based alloy 600. Residual stress, hardness, surface roughness, microstructure, and short-period oxidation behavior in untreated (UT) and WJCP-treated alloy 600 were characterized. A continuous oxide film was formed on the WJCP-treated surface after a short period of exposure, while it was discontinuous in the UT specimen. The change in oxidation behavior was attributed to the ultrafine grain and dislocation structure resulting from the WJCP treatment.