The cross-flow ultrafiltration of reverse micelles was investigated to examine the applicability of a membrane reactor for continuous enzymatic reaction. An ultrafiltration ceramic membrane module of tubular type was used to separate the Aerosol OT reverse micelles from the continuous phase of iso-octane. The rejection of reverse micelles as well as the permeation nux were measured at different concentrations of surfactant, water, enzyme and molar ratio of water to surfactant omega(o). The permeation nux decreased and the rejection of water increased with increase in the concentration of lipase, probably as a result of the higher enzyme mass adsorbed on the membrane. The rejection of reverse micelles also increased with increase in omega(o), which influences the diameter of reverse micelle. The permeation flux, however, could not be correlated solely with the parameter omega(o), and it depended on the concentration of surfactant itself when omega(o) was less than five. This direct influence of surfactant is supposed to be due to the adsorption of surfactant in the membrane which can change the hydrophobic property of the membrane.