X-ray line broadening techniques have been used to study the kinetics of crystallite growth in anatase hydrate powders between 680 and 900°C. The growth rate can be expressed by a fifth- power law with an activation energy of 46.2kcal/mol. These results are interpreted in terms of a surface diffusion mechanism. Different particle size results are obtained by scanning electron microscopy, suggesting that the latter technique measures aggregates of the fundamental crystallites.