Nanocrystalline Co-Ni thin films were synthesized by electrodeposition, at different current densities (J = 1, 2, 3 and 4 A/dm²), on Cu substrate from chloride-sulfate aqueous bath containing thiourea as additive agent. A study of the surface morphology of as plated deposits was accomplished by Scanning Electron Microscopy (SEM) technique. The SEM micrographs exhibit a rough and compact surface with a cauliflower-like appearance at lower current densities and a smoother surface with the rise of the current density. The evolution of crystalline phases of the obtained thin films was followed by X-ray diffraction (XRD) technique through the Rietveld refinement of the XRD patterns using MAUD software. For the Co-Ni thin film obtained at J = 1 A/dm², the obtained results reveal the formation of FCC and HCP structures: FCC (Cu), FCC Co(Ni), HCP (Co), HCP Co(Ni) and HCP/FCC Co(S). The Rietveld refinement of the XRD patterns (J = 2, 3 and 4 A/dm²) shows the absence of FCC (Cu) peaks and the formation of several FCC and HCP (Co) based structures. The rise of the current density accompanies an increase in the nucleation rate and causes a decrease of the crystallite size down to the nanometer scale. The root-mean square strain of different structures increases with increasing applied current density.