The structure of disordered and ordered titanium monoxide containing structural vacancies in both sublattices was studied by X-ray diffraction. The symmetry of the monoclinic Ti5O5 superstructure (space group C2/m) was analyzed. The type and channel of the TiOy–Ti5O5 disorder–order transition was determined. The distribution functions of Ti and O atoms in the metal and nonmetal sublattices of titanium monoxide were calculated. The specific heats of TiOy titanium monoxides (0.8 < y < 1.27) were measured by differential scanning calorimetry for the disordered and ordered states in the range from 340 to 600 K. The dependences of the specific heat, enthalpy, and entropy on the composition and structure of TiOy were found for the first time. A notable effect of the structural state on the specific heat was detected. In the indicated temperature range, the Cp(T) dependence is adequately described by a function that accounts for the Debye effect and the electronic specific heat. Key words: titanium monoxide, nonstoichiometry, disorder–order phase transition, Ti5O5 superstructure, vacancy channels, X-ray diffraction, differential scanning calorimetry, specific heat.