Membrane-supported liquid-liquid extraction is known as an interesting alternative to conventional extraction. With this technology, both liquid phases do not have to be dispersed, formation of emulsions hardly takes place and phase separation is not necessary. In biotechnology, extraction by means of aqueous two-phase systems (ATPS) is known as a very promising tool for the capturing of proteins and peptides. As both involved phases are water based, there is no undesired interaction between bio molecule and liquid phase. There also is only little difference in phase density. Therefore, the phase separation after extraction normally requires centrifugation. By applying an ATPS into a membrane contactor, extraction of biomolecules can be applied without phase separation. It could be shown that BSA and lysozyme could be extracted by means of ATPS with a membrane contactor without mixing and phase separation. However, extraction only took place if traces of a surfactant (Tween-20) were added to the ATPS, since then the used hydrophobic membrane (Liqui-Cel X40) was wetted from at least one of the two aqueous phases. Under these conditions, extraction could be repeated several times without any technical problems. With a dedicated experimental set-up, even kinetic data of the over all extraction could be generated. The combination of ATPS and membrane extraction enhances the advantages of both single technologies and makes this process an interesting alternative to down-stream purification steps such as chromatography.