The influence of inorganic filler TiO2 nanoparticles on the morphology and properties of polysulfone (PS) ultrafiltration membranes was investigated. PS/TiO2 composite membranes were prepared by a phase-inversion method. TiO2 nanoparticles modified by sodium dodecyl sulfate were uniformly dispersed in an 18 wt % PS casting solution. The addition of TiO2 resulted in an increase in the pore density and porosity of the membrane skin layer. The pore size distribution changed from the log-normal distribution to the bimodal distribution because of the presence of TiO2 nanoparticles, and some large pores were observed when the concentration of the filler was over 3 wt %. The skin layer was gradually thickened; meanwhile, the morphology sublayer changed from macrovoids to spongelike pores, in comparison with PS membranes without the filler. The addition of TiO2 also induced increases in the hydrophilicity, mechanical strength, and thermal stability. The ultrafiltration experiments showed when the concentration of TiO2 was less than 2 wt %, the permeability and rejection of the membrane was enhanced and then decreased drastically with a higher filler concentration (> 3%). (c) 2006 Wiley Periodicals, Inc.