Enzymatic hydrolysis of potato starch into maltose syrup in a tubular membrane reactor was studied. Hydrolysis and ultrafiltration conditions were determined in order to estimate the permeate flux and maltose concentration suitable for industrial production of maltose syrup. Experiments were made with different parameters such as: substrate: enzyme ratio, membrane porosity, transmembrane pressure. In a membrane bioreactor fungal α-amylase was able to produce maltose syrup with maltose and maltotriose content of 55-65% and 16-23%, respectively.