The work aims to strengthen the Ni-based plating and determine the effects of Al2O3 size on properties of the composite plating. Al2O3 composite platings in three sizes (micron, 50 nm and 30 nm) were prepared under optimum processing conditions taking hardness as evaluation criteria. Surface morphology, microhardness, wear resistance and corrosion resistance of the Al2O3 composite platings in three sizes were studied and analyzed. Surface morphology of the nanocomposite coating was smoother, denser and finer than that of the micron composite plating. The smaller the nanoparticles were, the denser the plating was. Microhardness, wear resistance, corrosion resistance and high temperature oxidation resistance of the nanocomposite plating were better than those of the micron composite plating and pure Ni plating. The surface of the nanocomposite plating was smoother and denser after heat treatment. The microhardness of the plating could be remarkably improved by heat treatment. The 50 nm and 30 nm composite plating exhibited the maximum microhardness of 461HV and 496HV at 400 ℃ and 500 ℃, respectively. Wear resistance of the nanocomposite plating was not obviously improved by heat treatment. The smaller the Al2O3 particles are, the better the performance of composite platings will be.