The optimal condition for the torrefacdon of oil palm mesocarp fiber was investigated by response surface methodology. Pelletizing properties of torrefied biomass were analyzed depending on torrefaction conditions. The elemental composition of torrefied biomass was influenced by the Severity Factor (SF) of torrefaction. The carbon content in the torrefied biomass increased from 48.02 to 54.83%, while the hydrogen and oxygen contents decreased with the SF. The calorific value of torrefied biomass ranged from 19.15 to 22.82 MJ kg(-1). This implied that the energy contained in the torrefied biomass increased by 5-19%, when compared with untreated biomass. The calorific value and weight loss in the biomass increased as the SF increased. The energy yield was high at a low SF, allowing for weight loss and calorific value. At a high SF, no pellets were made by torrefied biomass, or many defects were shown in the torrefied pellet, while the pellets were produced with good formation at a low SF. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.