Wood has been very useful in many fields due to its excellent properties. However, it also has less attractive characteristics, like high hygroscopicity and low bioconversion efficiencies. Heat treatment has been proved to improve these properties making lignocellulosic materials a stronger alternative to non-renewable sources to produce energy and other products. This study focused on the structural changes of heat treated poplar (populus) wood specimens treated under different temperature conditions. Nitrogen adsorption, pore size distribution and specific surface area of heat treated wood were studied. Increasing the temperature of treatment leads to a change on the characteristics of the nitrogen adsorption isotherms. The volume of pores for samples treated at higher temperatures is much greater comparing with samples below 400 oC BET specific surface areas were generally low for samples at temperatures until 400 oC, after this a great increase occurred while increasing temperatures up to 500 oC (413,06 m2/g).