Abstract: The sorption and desorption isotherms of standard particleboard were obtained in this study using the equilibrium moisture contents achieved by applying the gravimetric method of saturated salts at 35 degrees C and 50 degrees C in the water activity range of 0.11 to 0.89. The curves were fitted following the Guggenheim, Anderson and Boer-Dent model, and the isosteric heat of sorption was obtained by means of the Clausius-Clapeyron integration method. The results show that although particleboard has a thermodynamic behaviour which is qualitatively similar to solid wood, its hygroscopic behaviour is nonetheless different, as the monolayer becomes saturated by chemisorption before physisorption starts to prevail over chemisorption.