Polysulfone/polyaniline (PSf/PANI) ultrafiltration (UF) membranes were prepared via the phase inversion method using N-methyl-2-pyrrolidone (NMP) as the solvent and PANI emeraldine base particles as the additive, It was observed that when NMP was exchanged in an aqueous bath that was non-solvent for PANI, the PANI particles re-assembled into different conformations depending on the pH of the aqueous bath. Thus, PSf/PANI UF membranes were prepared using aqueous coagulation bath with various pH values. It was expected that altering the pH of the coagulation bath could affect the surface migration of PANI particles during membrane formation and tailor the morphology as well as separation performance of the membranes. The re-assembly process of PANI particles in acid/base aqueous solution was investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ultraviolet-visible spectroscopy (UV-vis). PSf/PANI membranes were characterized by SEM and water contact measurement. The separation properties of composite membranes were investigated in terms of water permeation and protein filtration. The results showed that the porosity and surface pore size of PSf/PANI membrane increased with increasing pH values of the coagulation bath. A substantial increase in water flux was observed for PSf/PANI membranes coagulated in base aqueous bath while an obvious decrease in water flux was observed for PSf/PANI membranes coagulated in acid aqueous bath. Changes in morphology and separation performance of PSf/PANI membranes were found out to be directly related to the re assembly process of PANI particles in aqueous bath at different pH values. The increase of membrane permeability with slightly scarifying rejection could be achieved by adjusting the pH of an aqueous bath during the preparation of PSf/PANI UF membranes. (C) 2014 Elsevier B.V. All rights reserved.