The available data on intrinsic kinetic parameters of wood char combustion is limited in the literature. The intrinsic reactivity of porous char particles reflects the variance in the pore structure resulted from various compositions of parent biomass or coal fuels. In this study detailed kinetic models for calculating the intrinsic reaction rate and the Arrhenius parameters in two combustion zones are developed for the char combustion. The influence of the parent fuel composition and the thermal treatment on the char oxidative reactivity observed on the char surface area and particle density are explored through a mathematical model of the char service area and density. A higher reactivity of the wood pellets than coal and enhanced reactivity with the increasing pyrolysis temperature were observed as well.