In the current study, the effect of colloidal copper nanoparticles on the deposition rate and hardness of Ni-Cu-P coating deposited by electroless method on L80 steel substrate was investigated. Copper particle size, microstructure, chemical composition, and hardness of the coating before and after heat treatment at different temperatures were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDS) analysis, and microhardness. The microstructure study by XRD showed that the Ni-Cu-P coating has an amorphous structure. The heat treatment at 400 °C transformed the structure from amorphous to crystalline and formed Niα, Ni3P, and Ni3.8Cu phases. The amount of copper nanoparticles in the coating 4.58 wt% was measured. The deposition rate of the Ni-Cu-P coating was 11 µm/h. Furthermore, the hardness of the coating increased from 738HV to 1300HV by performing heat treatment.