The aim of the present study was to thoroughly investigate the effect of alkali metal counter-ions (Li, Na, K and Rb) of PFSA on the formation, morphology and performances of polyvinylidenefluoride (PVDF)/perfluorosulfonic acid (PFSA-M) hollow fiber membranes. It is found that the homogeneous region in the ternary phase diagram of the PVDF-PFSA-M/NMP/H2O systems shrinks and the precipitation rate increases when varying the counter-ions of PFSA in the order of U, Na and K. The double finger-like structure and the cavities can be evidently developed with increasing the radius of the counter-ions of the spun PVDF/PFSA-M membranes. The pure water permeability (J(W)) and mean effective pore size of the PVDF/PFSA-M membranes first increase from counter-ion Li. Na to K and then slightly decrease for Rb. In addition, the highest J(W) value of 96.5 LM-2 H-1 bar(-1) was obtained for the PVDF/PFSA-K membrane with a MWCO of 86 kDa. XRD patterns and FTIR-ATR spectra verify the exclusive formation of beta crystalline phase structure in the as-spun PVDF/PFSA-M membranes. The PVDF/PFSA-Li membrane has better Young's modulus and tensile strength than that of other PVDF/PFSA-M fibers. (C) 2012 Elsevier B.V. All rights reserved.