For verifying the non-equilibrium reduction under microwave heating, authors investigated the reduction behavior of TiO2 using quadruple mass spectrometer during microwave(single-mode)/conventional(electric furnace) heating under vacuum of 10-5Pa. Under microwave heating at the position of Ç-field field maximum (We call it microwave H-field heating), ΔG has decreased compared with conventional heating. Meanwhile, we reheated the sample under microwave H-field field, ΔG was identical in conventional heating excluding over 1500°C. After heated, the sample structure changed to the nano-domain structure. Moreover, when we reheated the sample by microwave H-field field after conventional heating, ΔG was also identical in conventional heating excluding over 1500°C. The outcome suggests that the non-equilibrium reduction occurs in discrete system like powder.