Abstract: The microcrystalline Ni- and nanocrystalline Ni-based composite coatings incorporated with diamond nano-particulates were prepared making used of electrodeposition. The effect of the nano-diamond particulates on the surface morphology, microstructure, hardness, and wear-resistance of the two types of Ni-matrix coatings were investigated. Thus the Ni-matrix coatings with and without the nano-diamond particulates were characterized by means of X-ray diffraction and scanning electron microscopy. The friction and wear behaviors of the coatings sliding against AISI1045 steel under unlubricated condition in a ball-on-disc configuration were evaluated using a UMT-2MT friction and wear tester. The worn surfaces morphologies of the coatings were also analyzed by means of scanning electron microscopy. It was found that the incorporation of the nano-diamond particulates contributed to greatly increase the hardness and wear resistance of the microcrystalline Ni-matrix coating, but it had little effect on the hardness of the nanocrystalline Ni-matrix coating. Moreover, the nano-diamond particulates were harmful to the wear-resistance of the nanocrystalline Ni-matrix coating. The increased wear-resistance of the microcrystalline Ni-matrix coating in the presence of the nano-diamond particulates was attributed to the dispersive strengthening effect of the nnaoparticulates, which helped to increase the ability of the coating to resist plastic deformation and adhesion as well.