Rust in rust-prone steel is promoted in water by corrosive factors. Therefore, to prevent the formation of rust, it is necessary to eliminate various corrosive factors before plating or other rust prevention measures. In this study, we investigated improvement of the corrosion resistance of steel surfaces by mechanochemical-multifunction cavitation (MC-MFC) with a sodium hypochlorite solution and MFC in water. The compounds formed on the steel surface after MFC and MC-MFC were α-FeOOH and β-FeOOH. Furthermore, red rust was less likely to occur on the surface after MC-MFC; therefore, it was concluded that the amount of β-FeOOH was relatively high. In combined cycle tests conducted to evaluate the rust resistance, red and black regions were formed on the unprocessed and MC-MFC processed surfaces, respectively. The MC-MFC treated surface effectively suppressed rust formation because the amount of Fe compounds was less in the depth direction than on the untreated surface, as determined by glow-discharge optical emission spectroscopy analysis.