The effect of the milling energy and nonstoichiometry of cubic tantalum carbide TaCy (0.81 ≤ y ≤ 0.96) on the strain anisotropy of the crystal and the size of particles in nanocrystalline powders has been experimentally investigated using Xray diffraction. The functional dependence of the reduced broadening of diffraction reflections on the scattering vector, which takes into account the contributions of the size, strain, and inhomogeneous broadenings, has been obtained. The average size of coherent scattering regions and the crystallite microstrain accounting for the anisotropy of deformation distortions have been estimated. It has been shown that a more precise description of the experimental data on the broadening of diffraction reflec tions is achieved by the inclusion of the microstrain anisotropy and inhomogeneous broadening in the anal ysis.