Water removal in enzymatic ester synthesis is an important factor in determining the extent of the reaction. One of the methods of water removal is through the use of hollow fiber membrane reactors. When using such reactors with immobilized enzymes, it is important that the reaction is not hampered by mass transfer limitations on the membrane side. In this experiment, lipase from Candida rugosa was immobilized onto the lumen side of the cellulose hollow fiber membrane and air at a certain water activity (a(w)) were recycled through the shell side. The organic phase used was dodecanol dissolved in hexane. The effects of enzyme loading, the polarity of the organic phase, and the water activity of the extraction phase on the overall mass transfer coefficients (k(ov)) for the removal of water from a non-polar medium were investigated. The k(ov) values for the non-immobilized system were measured to be between 60.6 x 10(-9) and 100.3 x 10(-9) m/s when the concentration of the organic phase was varied from 0.1 to 1.0 M. The k(ov) values decreased by about 70% with the immobilized enzyme system, indicating that diffusion limitation occurred in the membrane matrix. Increasing the enzyme loading or varying the water activity on the gas side does not affect the values of k(ov) significantly.