Enzymatic hydrolysis is crucial in processing lignocellulosic biomass into valuable products in biorefineries. Due to the synergistic action of used enzymes the cellulose and hemicelluloses chains are digested into fermentable monosaccharides. It is known that the process efficiency can be improved by the separation of reaction end-products being cellulases' inhibitors. The work aimed to investigate the efficiency of enzymatic hydrolysis of corn stover and poplar wood biomass in a stirred dead-end membrane bioreactor, enabling continuous separation of end-products. Four UF membranes with different molecular weight cut-offs were tested, and PES 5 kDa was chosen as the most suitable. To pretreat biomass before hydrolysis, soaking in aqueous ammonia (SAA) and liquid hot water (LHW) methods were compared. The LHW treatment allowed for obtaining relatively high glucose contents (up to 73.7%). In turn, the SAA method led to high xylose contents up to 23.5%. In general, remarkable improvements (up to 72.6%) in monosaccharides contents in hydrolyzates after membrane bioreactor were observed. Only in the case of corn stover after SAA pretreatment, the reaction efficiencies in the membrane bioreactor were similar to those obtained in a batch mode with an improvement of 4.3%.