Poly(ethylenetarepthalate) (PET)-based polymer electrolyte membranes (PEMs) for fuel cells were successfully prepared by grafting of allyl methacrylate (AMA) and allyl acetate separately onto PET films under UV- radiation. A consequent selective sulfonation of the grafted films was performed by chlorosulfonic acid (ClSO¬3H) under milder condition. The sulfonation reaction proceeded at the grafted chains, as a result the grafted films successfully transformed to a PEM. It has been confirmed by titrimetric and gravimetric analyses as well as FTIR spectroscopy. The ion exchanges capacities (IECs) of the PEMs were studied by changing the degree of grafting and sulfonation. IECs of the PEMs prepared by grafting of allylmethacrylate (AMA) and allyl acetate onto PET were found in the ranges of 0.013-0.035 mmol/g and 0.03114-0.04125 mmol/g respectively. Water uptake, acid and hydrogen peroxide tolerance, tensile strength and proton transfer rate of the PEMs were studied. Electrical properties such as resistance, dielectric loss, and capacitance of the PEMs were also studied using impedance analyzer.