A novel proton conductor has been developed using ternary polymer blend. Polymer films cast-coated from solutions containing poly(acrylic acid), poly(vinyl butyral) and vinylidene-fluoride-based copolymer demonstrated higher ac conductivity than that of a Nafion ® recast film. The relationships between (i) polymer composition and membranous character and (ii) polymer composition and ac conductivity have been investigated. As a result, it has been proven that the ternary polymer film has good thermal stability and high proton conductivity. Based on that, an optimised polymer composition has been determined.