An intermediate material of a thermoplastic prepreg for a fuel cell separation plate comprises a hydrophobic thermoplastic resin film and a fiber base. The hydrophobic thermoplastic resin film has a degree of crystallization of 1 to 20%, a thickness of 3 to 50 μm, and (iii) a content of an electroconductive material of 1 to 20 wt. %. The film is laminated on at least one surface of the fiber base. The thermoplastic prepreg for a fuel cell separation plate is manufactured by pressurizing the thermoplastic prepreg intermediate material at a temperature higher than the melting point of the hydrophobic thermoplastic resin film. A fuel cell separation membrane manufactured using the thermoplastic prepreg intermediate material and thermoplastic prepreg is thin and light-weight, and have a good durability.