The paper considers the features and regularities of formation of Ni-Cu based diffusion coatings on the surface of steel products obtained as a result of diffusion metallization from the medium of low-melting liquid metal solutions. It was found out that a solid solution of Ni, Cu, Fe was formed in the main layer of coatings after applying the Ni-Cu coating on armco-iron, steel 20 and tool steel Kh12MF; it was characterized by approximately equal concentration of nickel and copper on the coating surface, it made 55 % Ni and 27 % Cu. As soon as the depth of the base layer increases, concentration of Ni and Cu in it gradually decreases, while the iron content also increases. During formation of Ni-Cu coatings on alloyed steels, selective diffusion of steel alloying elements deep into the coating is observed. It is established that the coatings have two layers -the main and the transition ones. At the same time, the maximal coating thickness constitutes 55 μm at the saturation temperature of 1150 °C and 6 hours duration. It was revealed that the main layer consists of Ni, Cu, Fe solid solution, also contains steel alloying elements and consists of columnar grains elongated in the direction of diffusion of the coating elements, as well as in its surface layer with thickness of about 5 μm. The layer of nano-scale grains with a cross-section size of 80-100 nm is forming. During formation of Ni-Cu based coatings, the phenomenon of displacement of the coating carbon and the steel alloying elements into the transition layer is confirmed; these carbon and steel elements do not interact with the coating elements.