Abstract: Ni-P-nanodiamond (ND) composite coatings were prepared by adding core-shell ND particles to electroless plating bath. Core-shell ND particles were coated with Al₂O₃ layer by using heterogeneous nucleation. The stability of colloidal particles in nickle solution was evaluated by sedimentation test. The effect of core-shell ND concentration in electrolyte, rotation speed of stirrer and heat treatment of coated powders on microhardness and wear of the coating were investigated. The friction and wear were evaluated on a pin-on-disk tribo-meter under unlubricated condition, while micro-morphology and composition of coatings were analyzed by scanning electron microscopy. The results demonstrate stable dispersions of coated core-shell ND particles in solution. The significant improvement in tribological properties of Ni-P-ND composite coatings was obtained under the condition of core-shell ND concentration of 4g/L, rotation speed of 500 r/min and heat treatment at 100℃ for 1h. The friction coefficient decreased by 60% and wear-resistance increased by 50% in contrast with pure Ni-P coating.