As a renewable source of energy, biomass is expected to play more prominent role in our future metallurgical applications as a sustainable energy and reductant source. In this respect, an understanding of the thermal decomposition of biomass is clearly of great importance because thermal degradation is always the first step in the conversion process. The present study investigates thermal decomposition of wood samples using an advanced computational thermal analysis method. With this method the apparent specific heats of selected biomass samples were estimated during continuous heating at 10°C/min for the temperatures of up to 600°C. The rate of change in the heat of reaction with respect to temperature (ΔH/ΔT) was determined from the measured data and the consequent heats quantified for each sample. The results indicated that biomass pyrolysis has an overall exothermic effect with an endothermic decomposition of its cellulosic component. The exothermic reaction of wood at higher temperatures was primarily affected by its lignin content and the char formation reactions.