The aim of the work was to define the physicochemical parameters of a reaction system that alter the effectiveness of a continuous recycle membrane reactor during potato starch hydrolysis. The enzymatic hydrolysis of starch in an ultrafiltration reaction system proceeded with a continuous decrease in the permeate flux, accompanied by an increase in dry substance content in both the permeate and retentate fractions. The decrease in the permeate flux was caused by an increase in feed viscosity. If a prehydrolysis process was conducted, it was possible to enzymatically hydrolyse potato starch in solutions with concentrations up to 20%. A quasi-steady state of starch enzymatic hydrolysis was reached in the ultrafiltration reaction system by alternately supplementing it with starch solution and water.