The dependence of the size of particles in the prepared nanocrystalline powders on the composi tion of nonstoichiometric compounds within their homogeneity intervals has been considered in terms of the highenergy ball milling model. It has been shown that the effect of nonstoichiometry on the milling mani fests itself in the concentration dependences of the main characteristics (parameters of the crystal structure, energy of interatomic bonds, elastic properties) of the milled nonstoichiometric compound. The results of model calculations performed for nonstoichiometric cubic niobium carbides NbCy have been compared with the experimental data on milling of the NbC0.93 carbide.