The polystyrene-DVB/PVDF alloy particles were prepared by pulverizing the polymerization product of styrene/DVB/PVDF in DMF, and then sulfonated with concentrated sulfuric acid to gain the cation exchange alloy powder, which was directly thermoformed by a hot-press machine to form the titled cation exchange alloy membranes with the structure of semi-interpenetrating polymer network. The effects of the polystyrene-DVB to PVDF mass ratio and the DVB content in the monomers on the physical and electrochemical properties of the prepared alloy membranes were investigated. While the Fourier transform infrared spectroscopy (FTIR) confirms the components of membranes, the scanning electron microscopy (SEM) reveals that the alloy membranes possess a uniform distribution of functional groups, and a more dense structure with the increases of DVB content and PVDF content. The optimal prepared membranes have the area electrical resistance values within 3.0-6.6 Omega.cm(2), obviously superior to the commercial heterogeneous cation exchange membrane, as well as the moderate water contents of 35-40% and the desirable permselectivity with a transport number more than 0.95. (C) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1220-1227, 2013