This study includes the development of a high heat-resistant FRP whose matrix is T_g-less epoxy resin which can be cured by anionic polymerization with potassium carboxylate salts as initiators. First, various epoxy resins with different chemical structures were evaluated to find an epoxy resin composition which has the least decrease in elastic modulus even at an elevated temperature. As a result, R, which is defined as the ratio of the modulus at 250°C to that at 25°C, exhibited the highest value of 44.5% in the combination of bisphenol A type epoxy resin with a multi-functional glycidyl ether derived from multi-functional phenols. The GFRP whose matrix was this T_g-less epoxy resin composition exhibited high heat-resistant property of R≥80% at 34 vol% of glass fiber content. The FRP had also excellent corrosion-resistance because the chemical structure of its matrix is hard to be hydrolyzed even under acidic or alkaline conditions.