The effect of the packing fraction of the powder layer of the starting material powder on the progress in the solid-phase reaction to produce indium tin oxide (ITO) using a microwave heating method was investigated using indium oxide and tin oxide powders; the electrical field and temperature distributions in the reactor were also numerically simulated. The electrical conductivity of the product powder is dependent on the packing fraction of the starting material and can be improved by reducing the packing fraction and increasing the air-feed to the powder layer, which increases the reaction temperature. Furthermore, reducing the packing fraction can equalize the radial disparity of the electrical conductivity since the starting material powder is fluidized and agitated by the introduction of air during microwave irradiation. These findings indicate that feeding air to the reactor increases the conversion and reaction rate and imparts radial uniformity to the reaction progress. It was also found that the simulated temperature distribution agrees qualitatively with the results of the experimental temperature measurements. The dependence of the reaction temperature on the packing fraction can be also expressed by the simulation. The simulation results suggest that the amount of heat generated per unit of powder volume can be used to evaluate the uniformity of the reaction progress and conversion to ITO. (c) 2013 Elsevier Ltd. All rights reserved.