Emeraldine base polyaniline (PANiEB), which is mostly soluble in N-methyl-2-pyrrolidone (NMP) and slightly soluble in water, was used as the additive to prepare polysulfone (PSf)/PANiEB membrane via immersion precipitation process. The behavior of PANiEB during membrane formation and the effect of PANiEB addition on membrane structure and performance were investigated. During membrane formation, a portion of PANiEB, located near the surface of the casting film, could diffuse out of the casting film along with NMP into the coagulation bath and act as pore forming agent. The other portion of PANiEB could remain in the prepared membrane and act as hydrophilic modifier. All the PSf/PANiEB membranes had higher porosity, larger surface pore size, more vertically interconnected finger-like pores and less macrovoids than PSf membrane. PSf/PANiEB membranes exhibited stable pure water flux during membrane compaction at 0.30 MPa TMP and slower pure water flux decline at 0.5 MPa TMP than PSf/polyvinylpyrrolidone (PVP) membranes. Pure water fluxes of PSf/PANiEB membranes were 1.7-2.8 times that of PSf membrane while rejection property including bovine serum albumin, egg albumin and trypsin rejections changed slightly. BSA ultrafiltration experiment showed that PSf/PANiEB membranes had higher flux and better antifouling property than PSf membrane. (C) 2011 Elsevier B. V. All rights reserved.