The effects polyethylene glycol 600 (PEG 600) and lithium chloride (LiCl) as additives on the preparation of cellulose acetate (CA) and silica (SiO2) blend ultrafiltration membranes were investigated in terms of water content, hydraulic membrane resistance, permeation performance, membrane morphology, and mechanical property. The addition of the additives into the casting solution changed the structure of the resultant membranes, which was believed to be associated with the change of the thermodynamic and kinetic properties of the system in the phase inversion technique. The pure water flux (PWF) of the membranes improved from 29.60 to 34.28 l m(-2) h(-1) when 5 wt.% LiCl and PEG was used as the additives in the pure CA membrane, respectively. The average pore size and porosity of the membranes were revealed by pore statistics and molecular weight cut-off (MWCO) studies using different molecular weight of proteins. Among the two additives, the membrane made from the casting containing PEG possessed the highest average pore size and porosity. The separation of proteins with the membranes was also studied. In particular, it was found that CA/SiO2 blend membranes with additives exhibit improved permeate flux of proteins. The fouling-resistant ability and the recycling potential of the OF membranes were found using bovine serum albumin (BSA) as model protein and the results are discussed. The results indicated that presence of pore formers (PEG and LiCl) in pure CA and all composition CA/SiO2 blend membrane, the total fouling resistance decreased resulting in enhanced flux recovery ratio which improved the life time membranes. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.