The integration of the reaction and separation in a multifunctional reactor unit for the enantioselective production of S-ibuprofen is studied, both experimentally and by kinetic modeling. The ultrafiltration by a commercially available polyacrylonitril membrane is used for the in-situ removal of the product. The application of the on-line ultrafiltration leads to a twofold increase in the overall productivity, that is due to the decrease of the deactivation and inhibition of the enzyme caused by the product. After initial decrease, probably caused by the fouling the fluxes through the membrane remain stable for a long period of time. The concept presents a promising option for other systems with conversion limited by the inhibitory effect of the products.