The evolution of the microstructure of nonstoichiometric vanadium VC0.875 and niobium NbC0.93 carbide powders subjected to high-energy ball milling is investigated by neutron diffraction. It is established that milling produces non uniform powders and two distinct fractions with differing microstructure can be identified in them. It is shown that the time-of-flight neutron-diffraction technique is promising for studying the microstructure of highly deformed nonstoichiometric carbides and for quantitative determination of the anisotropy of microstrains.