Abstract This study focuses on the mechanocatalytical process combining dilute acid pretreatment and mechanical processing driven by ball milling. Milled and hydrolyzed barley straw samples are subject to reducing sugar analysis by DNS assay and capillary electrophoresis. Optimization of the saccharification conditions was carried out with two different sulfuric acid concentrations, 0.5 mol kg⁻¹ and 1.0 mol kg⁻¹, and compared. A significant yield of total reducing sugar (53.4%) was obtained from barley straw impregnated with sulfuric acid (1.0 mol kg⁻¹) after milling for only 20 min. Glucose and xylose concentrations accounted for 3.5% and 11.3%, respectively. Strikingly, the present study indicates a significant impact of the internal milling vessel temperature in the mechanocatalytical conversion process of barley straw in addition to the mechanical parameters and the catalyst concentration.