Abstract: A glass fiber reinforced flexible composite material is obtained by dispersing or embedding glass fiber in a fluororesin, which is a graft copolymer obtained by grafting a crystalline fluoro-polymer to an elastomeric fluoro-polymer. For example, the graft copolymer is obtained by graft polymerization of vinylidene fluoride with an elastomeric copolymer of vinylidene fluoride, chlorotrifluoroethylene and an unsaturated peroxy compound. The composite material possesses the physical and chemical properties characteristic of fluororesins and is flexible and easily melt processable. Sheets of this composite material using a glass fiber cloth have a soft feel and can easily be joined by high-frequency welding.