Abstract A new type of charged micro-mosaic membrane can be synthesized by radiochemical grafting of styrene and methyl methacrylate onto Teflon FEP film, followed by selective chemical reactions; a pre-irradiation technique must be used. The effects of pre-irradiation dosage, film thickness, reaction temperature and time on graft copolymerization were studied by measuring the grafting percentage. In the case of cografting styrene and methyl methacrylate onto Teflon FEP film (F46 film), the total grafting percentage at different ratios of monomers was also given. The results showed that: 1. The conversion curve for the grafting process of styrene is similar to that of methyl methacrylate, but the time taken to reach the mximum grafting percentage is different. 2. At the initial stage, the grafting rate of methyl methacrylate is faster than that of styrene, but the time taken to reach the turning point is similar in both cases. After this, the conversion curve for methyl methacrylate levels out, whilst the grafting percentage for styrene slowly increases further. 3. The total grafting percentage of mixed monomer is lower than that of styrene or methyl methacrylate alone under the same conditions. After graft copolymerization the resulting copolymers were saponified by a water—alcohol solution of sodium hydroxide in the presence of dioxane to obtain COO − type of cation exchangeable groups, chloromethylated by chloromethyl ether and then quarternized in aqueous trimethylamine to obtain −N +(CH 3) 3 anion-exchangeable groups. Some electrochemical properties of the above mentioned membranes were determined.