The thermodynamic properties of the Co-Cr-Mo ternary system have been described. Available experimental data on the system have been assessed and applied to optimize the parameters used in the thermodynamic models within the Calphad method. Meanwhile, samples were made by the powder metallurgical process and heat treated (sintered) at 1573 K to investigate the phase diagram data related to the intermetallic phases, such as σ, μ and R phases present in the system. With the optimized thermodynamic description, we are able to fit most of the experimental data in the literature and from this work. However, the one phase field of R is too narrow in the present description. Furthermore, at 1573 K the extension of the phase boundary of σ toward the Co corner needs to be improved. In addition, the calculated phase diagram at 1573 K shows a fcc-bcc-σ three-phase equilibrium near the Co-Cr binary side. This is not shown in the experimentally determined ternary phase diagram but is necessary in order to match the recent data on the Co-Cr binary system.