Sorption isotherms and isobars of energetic variety of willow Salix viminalis in a wide range of temperature and water activity were determined. In order to investigate sorption isobars a specially constructed set-up was built. The sorption isotherms were determined in the water bath and Clsorp water sorption analyser. The experimental data were compared with the literature data. It was found out that water activity of willow as a function of temperature and moisture content can be described by one generalized equation. The equation can be then used for the purpose of prediction of sorption equilibrium during wood drying process in a wide range of temperatures and moisture contents. (c) 2007 Elsevier Ltd. All rights reserved.