The Psf-PPSS-TPA composite cation exchange membrane consist of Psf(polysulfone)-PPSS (polyphenylenesulfidesulfone) block copolymer with TPA (tungstophosphoric acid) is prepared to apply for a separator in the all-vanadium redox flow battery. The membrane properties such as membrane resistance and ion exchange capacity, and thermal stability are investigated. The prepared Psf-PPSS-TPA composite cation exchange membrane showed higher thermal stability than Nafion117. The lowest membrane resistance of the prepared Psf-PPSS-TPA composite cation exchange membrane measured in 1 M (mol/dm3) H2SO4 aqueous solution was 0.94 Ωcm2 at 0.5 g of TPA solution. The performance properties of the all-vanadium redox flow battery (V-RFB) using the prepared cation exchange membrane are measured. The electromotive force, open circuit voltage at state of charge (SOC) of 100%, was 1.4 V. This value meets a theoretical electromotive force value of the V-RFB. The measuring cell resistance in charge and discharge at SOC 100% were 0.26 Ω and 0.31 Ω, respectively. The results of the present study suggest that the prepared Psf-PPSS-TPA composite cation exchange membrane is well suited for use in V-RFB as a separator.