A novel proton conducting polymeric gel membrane that consists of poly(ethylene oxide)-grafted-poly(methacrylate) (PEO-PMA) with poly(ethylene glycol) dimethyl ether (PEGDE) as a plasticizer doped with aqueous phosphoric acid (H3PO4) has been prepared and its physicochemical properties were studied in detail. The ionic conductivity was dependent much on the concentration of H3PO4, the immersion time, and content of the plasticizer. This type of proton conducting polymeric gels shares not only good mechanical properties but also thermal stability. Maximum conductivities up to 2.6 x 10(-2) S cm(-1) at room temperature (25 degreesC) and 2.8 x 10(-2) S cm(-1) at 70 degreesC were obtained for the composition of the polymer matrix to the plasticizer as 35/65 (in mass) after the H3PO4 doping from the aqueous solution with 2.93 mol 1(-1). FT-IR spectra showed that these high proton conductivities are attributed to the presence of excesses free H3PO4 in the polymeric gel in addition to the hydrogen-bonded H3PO4 to the polymer matrix.