The removal of phenol and o-cresol from water by a hybrid process of clay adsorption and ultrafiltration (clay-UF) was studied. Batch adsorption equilibrium experiments showed that the amount of adsorption for phenol and o-cresol decreased in the order kaolin > montmorillonite at an equilibrium pH (pH(e)) of 9.1. The clay-UF experiments were performed as a function of clay dose, solution pH, and transmembrane pressure. The role of pH in clay-UF process mainly depended on the acid-base nature of phenols and clays, and the charge of UF membrane. The rejection of phenol increased with increasing pH(e) and had a maximum at pH(e) = 8.2 with kaolin but at pH, = 9.1 with montmorillonite. The rejection of o-cresol also increased with increasing pH, and had a maximum at pH(e) = 9.2 with kaolin but at pH(e) = 10.2 with montmorillonite. Such differences between solute rejections depended on the pK(a) of the solutes, zeta potential of the clays, and surface charge of the membrane. The amount of soluble organics adsorbed onto the surface of membrane was negligible and the flux slightly decreased with increasing transmembrane pressure. (c) 2005 Elsevier B.V. All rights reserved.