Organic-inorganic hybrid membranes were fabricated by solution casting using different ratios of cellulose acetate (CA) and zirconia (ZrO2) in N,N'-dimethylformamide (DMF). The addition of ZrO2 microparticles in the CA matrix was varied from 0 to 7 wt.%. The developed membranes were characterized for ultrafiltration (UF) performance, mechanical stability, morphology and fouling-resistant ability. It is found that the pure water flux increases from 15.6 to 46.7 lm(-2) h(-1) while the tensile strength decreases from 2 to 1.4 N/mm(2) with addition of zirconia from 0 to 7 wt.% to pure CA, respectively. Morphological studies indicate that the CA:ZrO2 hybrid membranes possess asymmetric structure with ultra scale pores. From the pore statistics analysis, it was seen that the CA:ZrO2 (6:4 ratio) hybrid membranes have an average pore radius of 47.52 angstrom compared to 26.88 angstrom of pure CA membrane. It was found that the hybrid CA:ZrO2 membranes exhibit higher permeate flux for the separation of different molecular weight proteins compared to pure CA membrane. It has been demonstrated that the fouling-resistant ability and the recycling property of CA:ZrO2 hybrid membranes are enhanced due to the high flux recovery ratio with the addition of ZrO2 in the casting solution. (C) 2010 Elsevier B.V. All rights reserved.