<p>Experimental investigation of the phase equilibria in the Ce-Co-Cu ternary system was conducted via the equilibrated alloy technique, utilizing x-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). Ten binary intermetallic compounds, CeCo₂, CeCo₃, Ce₂Co₇, Ce₅Co₁₉, CeCo₅, Ce₂Co₁₇, CeCu₂, CeCu₄, CeCu₅, and CeCu₆, were confirmed, and no ternary intermetallic compounds were detected. It was found that the continuous solid solution phase Ce(Co, Cu)₅ was formed between the CeCo₅ and CeCu₅ binary intermetallic compounds due to having the same crystal structure. The solid solubilities of Cu in CeCo₂, CeCo₃, Ce₂Co₇, Ce₅Co₁₉, and Ce₂Co₁₇ as well as that of Co in CeCu₂, CeCu₄, and CeCu₆ were measured. Furthermore, a thermodynamic assessment of the Ce-Co-Cu ternary system was performed via the calculation of phase diagrams (CALPHAD) approach, incorporating both the experimental data obtained in this study and available literature results. The calculated isothermal sections exhibit good agreement with the experimental observations. Consequently, a set of self-consistent thermodynamic parameters has been acquired, providing a solid foundation for developing a thermodynamic database for Sm-Co-based permanent magnets containing abundant rare-earth and transition metals.</p>