The aim of this paper was to investigate the microwave dielectric properties of corn stover at 915 and 2450 MHz from room temperature to 700 degrees C under nitrogen (N-2) environment. Cavity perturbation method was used to measure the dielectric constant and loss factor. The heating process was divided into three distinct stages, namely drying, pyrolysis, and char stage. Dielectric properties during drying and pyrolysis stages were inversely proportional to the temperature, whereas directly proportional to the temperature in char stage. The maximum microwave penetration depth of 8.5 m was obtained at 392 degrees C and 915 MHz, just at the end of the pyrolysis reaction zone. The experimental data were fitted using regression fit and based on this the dielectric properties model related to the temperature was developed. (C) 2015 Elsevier B.V. All rights reserved.