Polyvinylidene fluoride (PVDF) membranes were prepared via a thermally induced phase separation method with a mixed diluent (dibutylphthalate/dioctyl phthalate). The effects of PVDF concentration and cooling bath temperature (CBT) on the structure and properties of the membranes were investigated. Scanning electron microscopy photos showed that the cross-section of all the membranes, regardless of PVDF concentration and CBT, presented a bi-continuous structure with the spheruliitic pattern; moreover, Hie spherulitic patterns became clear gradually from the top surface to the bottom surface, and the top Surface was denser than the bottom surface. As a result, all the membranes exhibited an asymmetric structure. The membrane property measurement indicated that, as PVDF concentration increased from 25 to 35 wt %, the pure water flux (PWF) decreased from 342 to 80 L m(-2)h(-1), and the porosity decreased slightly, whereas the minimum bubble point pressure (BPP) increased, which indicates maximum pore size decreased. In addition, with the increase in CBT, the PWF increased, but, the minimum BPP and porosity decreased. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:1213-1219, 2009