In this work, three nickel-cobalt-phosphorus composite coatings co-deposited with particles of silicon carbide of three different sizes (40, 200, and 800 nm) were prepared on aluminum alloys using electroless deposition.The fabrication process of composites has been discussed, and the effect of the particle size of silicon carbide on microhardness and corrosion resistance of composites has been studied.The mor-phology, composition, microstructure, microhardness, and corrosion resistance of deposits were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Vickers hardometer, and electrochemical workstation, respectively.The results reveal that the particle size has not much effect on the deposition rate of coatings; however, the coating codeposited with smaller particles has greater incorporation amount of particles in number density, less porosity, and finer grains.Furthermore, the incorporation of smaller particles leads to higher hardness and better corrosion resistance of coatings.