This paper was dedicated to evaluate the impact of thermal-expansionary pretreatment on the quality of hydrolysate and on biogas yield. An aqueous suspension containing 5% wt. of wheat straw was treated under process temperature 170-200 degrees C with residence time 0-60 min. It has been proven that the organic biomass loss of straw, the rate of disruptions in its microstructure, COD, glucose and acetic acid yields in the liquid phase of hydrolysate increased with an increasing process temperature and residence time, while acidity decreased. This technology has also significantly increased methane yield. A maximum increase of 41% was reached at process temperature 170 degrees C and residence time 20 min. Nevertheless, based on energy balance of the treatment, it was determined, that heat of regeneration is lower than heat needed to reach process temperature. An addition heat source must be therefore installed in the technology. (C) 2014 Elsevier Ltd. All rights reserved.