In the study, polyaniline (PANI) nanoparticles were used as polymeric additives in order to improve polyethersulfone (PES) structure and performance. A major role of PANI nanoparticles in PES membranes is to improve the hydrophilic properties and permeability of the substrate membrane. The central composite design (CCD) of the response surface method (RSM) was used for the optimisation of blended PES/PANI membranes. The objectives were to obtain the optimum operating variables and to observe interactions among the variables. The factors considered were the PES concentration, PANI concentration and evaporation time during the casting process, while pure water permeability, salt rejection and contact angle values were considered as the responses. The design of experiment (DoE) managed to develop models that related the responses with the operating variables which were further analysed by analysis of variance (ANOVA). The optimal conditions were 18.33 wt.% PES, 0.75 wt.% PANI and 1.34 min of evaporation time with the predicted results of water permeability, salt rejection and contact angle of 62.2 L/m(2) h bar, 32.4% and 54.95 degrees, respectively. The interaction graph shows that there was a strong interaction between the variables of PES concentration (A), PANI concentration (B) and evaporation time (C). With additional characterisation, the optimised membrane showed an improvement in the membrane structure when observed by SEM. The addition of nanoparticles evidently increased the membrane surface roughness, as observed in the AFM images. The membrane pore size distribution was also obtained from the AFM images which showed a difference between the control (1-6 nm) and blended (2-40 nm) membranes. The membrane surface charge showed that the blended membrane has the highest charge at low and high pH with iso-electric point at pH 3 while there is no iso-electric point obtained for a controlled membrane. (c) 2012 Elsevier B.V. All rights reserved.