A study has been made of the order-disorder phase transformations in the homogeneity region of the VCy nonstoichiometric cubic vanadium carbide (0.66,y,0.88). It has been established that an ordered V6C5 phase with monoclinic ~space group C2/m) or trigonal (P31) symmetry, and a cubic ~space group P4332) ordered V8C7 phase can form in the VCy carbide below 1450 K, depending on the actual composition. The effect of off-stoichiometry and structural vacancy ordering on the specific heat of the VCy carbide has been investigated. The temperatures and heats of the reversible order-disorder equilibrium transitions have been determined. The ordering in the VCy carbide is shown to be a first-order phase transition. An equilibrium diagram of the V-C system taking into account ordering in the nonstoichiometric vanadium carbide has been constructed.