Extractive ultrafiltration (EUF) of valeric acid from aqueous solutions with tri-n-butyl phosphate dissolved in kerosene, at two different phase ratios and using two ceramic membranes, was studied. The membranes used were ZrO2 supported on ct-alumina and ZrO2 + TiO2, supported on carbon with an average pore size of 20 and 45 nm, respectively. Permeation rates and degree of extraction were determined under three different modes of operation of the membrane unit: total recirculation, permeate removal, and continuous operation.