Novel cation-exchange nanocomposite membranes was fabricated by insitu formation of zinc oxide nanoparticles in a blend containing sulfonated polyvinylchloride and sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) by a simple chemical method. Also, some nanocomposite samples were prepared by incorporation of previously synthesized ZnO nanoparticles into the casting solution (ex-situ method). The prepared nanocomposite samples and nanoparticles were characterized by several techniques including water contact angle measurements, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The water contact angle measurements confirmed the increased hydrophilicity of the nanocomposite membranes. The SEM surface microphotographs indicated that ZnO nanoparticles were uniformly dispersed throughout the polymeric matrix. The influence of additive concentration on electrochemical and physicochemical properties of prepared ion-exchange nanocomposite membranes was studied. Various investigations revealed that the in-situ preparation of ZnO nanoparticles in the membrane structure had a considerable effect on the membrane efficiency and could improve the transport properties.