Plastic optical fibers comprising as a core component a polymer predominantly containing methyl methacrylate and as a cladding component a copolymer lower in the refractive index than the core component, the plastics optical fibers being characterized by performing conjugate spinning with use of the cladding component which is vinylidene fluoride-tetrafluoroethylene copolymer having incorporated therein 5 to 50% by weight of a polymer predominantly containing methyl methacrylate.