Wheat straw was pretreated with a thermomechanical process developed in our laboratory to increase the enzymatic hydrolysis extent of potentially fermentable sugars. This process involves subjecting the lignocellulosic biomass for a short time to saturated steam pressure, followed by an instantaneous decompression to vacuum at 50 mbar. Increasing of the heat induced by the saturated steam result in intensive vapour formation in the capillary porous structure of the plant material and the subsequent release of the pressure to vacuum allows fixing the structure. The process parameters tested in this study were the processing pressure between 3 and 7 bar and the particle size of crushed wheat straw. Enzymatic hydrolysis was performed on the pretreated solids by celluclast (1.5L). The results showed that the hydrolysis yield of wheat straw treated at pressure levels of 3, 5 and 7 bar for a processing time of 15 min was strongly improved compared to hydrolysis yield of un-pretreated wheat straw.