Super high hardness Ni-B-Sc coating was fabricated by electrodeposition for the first time. The effect of Sc on the structure and properties of Ni-based coating was investigated. The results show that the Ni-B-Sc coating exhibits a typical nanocomposite structure, in which the nanocrystalline Ni2Sc phase is embedded in the nanocrystalline Ni matrix, where nanocrystalline Ni around nanocrystallites Ni2Sc exhibits a fine-grained structure. The nanocomposite structure with nanoscale stiffer phase (Ni2Sc) embedded in the nanoscale ductile phase (Ni), significantly improve the hardness of Ni-B-Sc coating to 1484 Hv. The increased grain boundaries, phase boundaries and hard Ni2Sc particles cause the obvious increase in hardness as well as wear resistance of the coating.