The paper concerns a model analysis of bioreactor in which organic phase is a reservoir of the hydrophobic substrate that diffuses to biocatalyst layer immobilized on the membrane surface. Membrane keeps the water phase and organic phase separated. An influence of process parameters as the biocatalyst layer' thickness and mass transfer coefficients was shown. It was presented that under some process parameters the layer can be supported with substrate also from the water phase. The analysis of the process parameters influence on product purity in water phase was made.