In this study, we examine the reduction behavior of TiO2-x, during microwave irradiation at the maximum point of the H field in a single-mode cavity (H-field irradiation). The reduction of TiO2-x was greater and the decrease in the activation energy (E-a) for reduction was higher when microwave irradiation was used than when conventional heating was used. TiO2-x was decrystallized and formed a nanodomain structure with a 5-10 nm particle size. From these results, we determined the amount of microwave energy distributed as activation, kinetic, and thermal energies.