Super hard Ni-B/diamond composite coatings were prepared by electrodeposition. Such extreme hardness (ca. 2500 Hv) was ascribed to a large content of diamond particles and hardness of Ni-B matrix. Thermal treatment of the coatings resulted in the formation of Ni-B alloys, which led to increase in film hardness. This method is much simpler than previously reported methods for preparing hard coatings.