Torrefaction is a thermal pretreatment of biomass whose aim is to eliminate technical barriers of the biomass as an energy source. In this process, the raw biomass is heated in an inert atmosphere at temperatures of 200–300 °C and a low heating rate. Its purpose is converting the biomass into a carbonaceous material with improved physicochemical properties. The aim of this study was to assess the effect of torrefaction conditions on the thermal properties of a Colombian woody biomass.The results show that temperature and residence time torrefaction conditions presented a statistically significant effect on the thermal degradation of the biomass cellulose component and weight loss. In both responses, the temperature effect was higher than residence time. Besides, the residence time effect on the chemical transformation of the biomass increased when the torrefaction was more severe. TGA oxygen reactivity was measured and it was found considerable changes as the conversion of the biomass increase: high reactivity at the beginning of the oxidation reaction and diminution during the final stage of char oxidation.