Aluminum alloys are widely used in the aerospace and transportation industries, but the corrosion resistance is insufficient in long-term service especially in the high salinity environment. A ceramic coating composed of ZnO nanoparticles is demonstrated to significantly improve the corrosion resistance of the Al alloys. Owing to the similar chemical activity of Zn and Al, ZnO particles fuse into Al₂O₃ in the micro-arc during plasma electrolytic oxidation (PEO) rendering the coating compactness. The formation mechanism of the PEO coating is investigated and discussed. The corrosion current of the ZnO modified PEO coating is 4 orders of magnitude less than that of the LY12 substrate. Immersion tests performed in 3.5 wt% sodium chloride show that incorporation of ZnO prevents destruction and dissolution of the PEO coating in the high salinity environment.