Flat sheet asymmetric polysufone (PSf) membrane and PSf/clay nanocomposite membranes with different clay contents were prepared by the nonsolvent induced phase inversion method. N,N-dimethyl acetamide, deionized water and LiCl were used as a solvent, a coagulant and a pore forming agent, respectively. The morphology and structure of membranes were analyzed by scanning electron microscope, transmission electron microscope and X-ray diffractometer. The performance of the membranes was evaluated in terms of pure water flux (PWF), protein rejection, porosity, contact angle, tensile strength and elongation at break. Results showed that clay had a good dispersion in the PSf matrix. The addition of clay additive could improve the hydrophilicity of the membranes and increase the ratio of large pore in the skin layer. PWF and porosity of membranes increased with the increase in clay content. With increase in clay content from 0 wt.% to 6 wt.%, the PWF increased from 199 L.m(-2).h(-1) to 263 L.m(-2).h(-1). The tensile strength attained its maximum when the clay content was 3 wt.% and the value was 5.34 MPa. Clay had high stability in the nanocomposite membranes. (C) 2012 Elsevier B.V. All rights reserved.