Torrefaction is a thermo-chemical process, which is also referred to as a mild pyrolysis carried out at a relatively low temperature ranging from 200 to 300 degrees C. During the torrefaction process, the lignocelluloses materials, such as cellulose, hemicelluloses, and lignin, undergo degradation, with the maximum degradation belonging to hemicelluloses. The present research focuses on torrefaction of the flax straw under laboratory scale. Thermo gravimetric analyzer was used to study the effect of temperature, particle size, and residence time on the torrefaction of flax straw. Proximate analysis of the char remained after torrefaction showed a significant increase in fixed carbon and ash content and a noticeable decrease in the moisture and volatile content with an increase in the temperature. Ultimate analysis was also performed for the product char. The results of ultimate analysis showed that the maximum carbon and heating value obtained were about 61% and 24 x 10(3) kJ kg(-1), respectively, for higher particle size (1,200 mu m) and at higher temperature (300 degrees C). The kinetic analysis showed an activation energy of 76.64 kJ mol (1) for the particle size of 925 mu m and for the residence time of 60 min. The experimental results of the torrefaction of flax straw indicate that the temperature has a greater effect on torrefaction process than the residence time and the particle sizes chosen for this study.