Flexible printed circuit base materials of this invention are composed of at least one layer of polyimide resins of low thermal expansion, at least one layer of polyimide resins of high thermal expansion with a higher linear expansion coefficient than that of the foregoing polyimide resins, and at least one layer of a conductor, highly reliable in dimensional stability to temperature changes, adhesive strength, and flatness after the etching, easy to work with in protection of the circuits made by etching.