The interaction between V2O5 and Bi2O3 and the evolution processes of lattice oxygen from their physical mixtures and a binary oxide (BiVO4) have been studied by thermal gravimetric analysis. The source of lattice oxygen was Bi2O3, and it was more easily evolved from the physical mixtures especially of a V:Bi = 1:1 mole ratio than respective single metal oxides or the binary oxide. When the physical mixtures of V2O5-Bi2O3 are heated at low temperatures which do not cause phase transformation of oxides, they can evolve or absorb oxygen reversibly. The reoxidation of reduced oxides proceeded much faster than the evolution of oxygen. The effective contact between two oxide phases appeared to be an important factor for the synergy between two phases in the evolution of lattice oxygen.