The phase relationships of the Ti-Mn-Mo ternary system on the Ti-Mn side at 900 and 1000 °C were experimentally studied based on microstructure and phase constituents from the equilibrated alloys using electron probe microanalysis, scanning electron microscopy, and X-ray diffraction. The solubilities of Mo in the βTiMn, TiMn₂, TiMn₃ and TiMn₄ phases of the Ti-Mn system were measured. A three-phase region and seven two-phase regions were experimentally determined. No ternary compounds were found. Based on the experimental data and the thermodynamic descriptions of the three binary sub-systems available in the literature, a set of thermodynamic parameters of the Ti-Mn-Mo ternary system was obtained. The calculated isothermal sections and vertical sections agree well with the experimental results. The calculated liquidus projection and invariant reaction scheme of the Ti-Mn-Mo ternary system are also presented. The present work can provide essential experimental and thermodynamic data for the design of biocompatible medical titanium alloys.