Highly porous electrospun nanofibrous membranes have gained considerable interest in water filtration applications. To understand the effects of electrospun nanofibrous structures on the filtration performance, a series of nanofibrous membranes with different fiber diameters, diameter distributions and membrane thicknesses were prepared and studied. The results indicate a strong correlation between the physical parameters of the membrane and the filtration performance. For example, a thicker membrane with a smaller average fiber diameter greatly favors the formation of a smaller pore size and narrower pore size distribution, although the influence of the membrane thickness is relatively limited. Based on successful control of the total composite structure (electrospun polyacrylonitrile (PAN)/non-woven polyethylene terephthalate (PET)) containing the electrospun layer thickness of 200 +/- 10 mu m and a mean fiber diameter of 100 +/- 20 nm, a high flux microfiltration (MF) membrane with a maximum pore size of 0.62 +/- 0.03 mu m and a mean pore size of 0.22 +/- 0.01 mu m was obtained. The PAN/PET nanofibrous MF membranes performed significantly better than the commercial MF membrane of the same mean pore size (0.22 mu m), with two to three times higher flux (similar to 1.5 L/m(2) h). The nanofibrous MF filter could maintain a very high rejection ratio of micro-particle and bacteria (LRV = 6). The results suggest that electrospun nanofibrous membranes are excellent materials for high-flux MF applications. (C) 2012 Elsevier B. V. All rights reserved.