Abstract <p>The method of subcritical and supercritical ethanolysis was used to determine its impact on the degree of fermentolysis of wheat straw polysaccharides and the yield of sugars. The heat treatment of raw materials in ethanol was performed in the temperature range of 130–355°C (30 MPa, 10 min). The intensity of biomass delignification and hydrolysis of straw polysaccharides during processing is determined by the temperature. Chemical processes occurring in the wheat straw biomass under subcritical ethanolysis conditions can contribute to the enzymatic hydrolysis of polysaccharides of technical cellulose and are associated with the destruction of easily hydrolyzable pentosans and lignin. Upon the transition to the supercritical region, the intensity of hydrolysis of straw polysaccharides increases, resulting in an increase in the yield of the fraction of water-soluble compounds at 355°C to 14.5% dry mass and a decrease in the yield of insoluble straw residue (technical cellulose) to 26%. Under these conditions, cellulose is the main source of soluble carbohydrates. The low yield of technical cellulose obtained at ethanolysis temperatures above 285°C and the high content of lignin in it make it unsuitable for the enzymatic production of sugars. In the temperature range of 200–250°C, the yield of technical cellulose was 77–87% dry mass and the yield of sugars during its enzymatic hydrolysis was 27–33% dry mass. The results substantiate the possibility of using subcritical ethanolysis as an activation method for the enzymatic hydrolysis of straw cellulose.</p>