The purpose of this research is to determine the reactivity of a sample of high carbon fly ash obtained from a circulating fluidized bed (CFB) gasification system and benchmark it against three other chars prepared at different pyrolysis temperatures in a laboratory drop tube furnace (DTF). Isothermal and non-isothermal thermo-gravimetric (TGA) experiments were used to determine sample reactivities. Structural analysis tests were carried out to establish the influence of the pore characteristics and Scanning Electron Microscope (SEM) pictures were taken for sample morphology. In-spite of high (BET) surface area and pore volume; reactivity parameters such as activation energy, kinetic rate coefficient, half life, burnout temperature and time proved the fly ash to be the least reactive. The low reactivity is associated with its carbon thermal deactivation. Non-isothermal tests also show the fly ash to be heterogeneous in composition. Of all the samples, the char prepared in the laboratory at the lowest pyrolysis temperature was the most reactive. (C) 2011 Elsevier B.V. All rights reserved.