Anatase titanium dioxide was annealed under hydrogen atmosphere up to 800°C for several hours. The diffuse reflection spectra and X-ray diffraction were measured for the annealed powders. The changes in reflectance and conversion ratio to rutile depending on annealing conditions indicate that the contact of the powder with hydrogen in the temperature range of 400-700°C results in the formation of oxygen vacancies on the surface of the anatase powder. On the basis of the insignificant decrease in lattice volume depending on annealing temperature, there is a probability that other lattice defects could be formed. The transformation to the rutile phase was observed at temperatures higher than 650°C.