This study examined acid-catalyzed mechanocatalytic pretreatment of birch sawdust without a separate impregnation step. Catalyst amount and pretreatment time were the key variables. Pretreated material was mixed with water for hydrolysis (100 °C, 60 min). The efficient release of total reducing sugars from birch sawdust is significant to the path towards biofuels and biochemicals. Based on the results, the structure and surface of birch sawdust changed as a function of mechanocatalytic pretreatment. Milling time caused significant transformations in birch structure and also increased the yields of reducing sugars. The highest yield of total reducing sugar from pretreated sawdust was 23.0% after 30 min of hydrolysis with 1.0 mmol/g acid catalyst, whereas the highest glucose yield was 23.8 g/kg (1.5 mmol/g catalyst, 60 min) and the highest xylose yield was 37.5 g/kg (1.0 mmol/catalyst, 30 min). Overall, acid-catalyzed mechanocatalytic treatment seems to improve sugar yields from birch.