Polyethersulfone ultrafiltration membranes prepared via immersion precipitation were modified by TiO2 nanoparticles and UV irradiation. Three sets of membranes, i.e. TiO2-entrapped membranes, UV-irradiated TiO2-entrapped membranes and UV-irradiated TiO2-deposited membranes were prepared. The membranes were characterized by contact angle, SEM, FTIR, cross-flow filtration (pure water flux and milk water permeation) and antifouling measurements. The initial flux of TiO2-entrapped membrane was lower than the initial flux of neat PES membrane. However, the former membrane showed lower flux decline compared to the neat PES membrane. UV-irradiated TiO2-entrapped membranes represented higher flux and higher antifouling properties compared to TiO2-entrapped membranes. Contact angle measurement, FTIR and surface SEM image indicate that the TiO2 nanoparticles uniformly settled on the membrane surface by dipping the membrane into the TiO2 colloidal suspension. Flux behavior of 0.03 wt.% UV-irradiated TiO2-deposited membrane indicated higher performance and antifouling properties. TiO2 colloidal suspension with 0.03 wt.%, 15 min immersion and 15 min UV irradiation with 160 W lamp were determined as the optimum conditions for modification of PES membrane. Finally, a comparison between UV-irradiated TiO2-entrapped and deposited membranes proved that coating TiO2 on membrane surface is a superior technique for the modification of PES membranes to minimize membrane fouling. (C) 2008 Elsevier B.V. All rights reserved.