Novel polyaniline (PANI)/phosphomolybdicacid (PMA) nanoparticles were prepared by simple protonation method and used to enhance the antifouling property of polyethersulfone (PES) ultrafiltration membranes. The prepared nanoparticle size around 30 +/- 3 nm was confirmed by transmission electron microscopy and scanning electron microscopy analyses. Complete PMA incorporation with PANI was evaluated by Fourier transform infrared spectroscopy analysis. The surface charge of nanoparticles are average value is of -46 mV. The contact angle, water flux and flux with rejection of protein of all membranes increased by increasing nanoparticle concentrations in the range of 0, 2, 3, 5 and 7 wt.% into casting solution. Compared to pure PES membrane, the PES-PANI/PMA membrane exhibits better antifouling performance with very high (>98.8%) protein rejection rate. Especially, the 3 wt.% PANI/PMA nanoparticles incorporated membrane shown superior results than other membranes. The roughness of PES-PANI/PMA membranes are remarkably enhanced due to the drastic enrichment of nanoparticle segments on the membrane surface. Bovine serum albumin (BSA) was used as a model protein to investigate the protein adsorption resistivity and permeation properties of all membranes. BSA ultrafiltration experiment showed that PES-PANI/PMA membranes had higher flux and better antifouling property than PES membrane. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.