The effects of dye doping on ferroelectricity in vinylidene fluoride and trifluoroethylene copolymers have been investigated mainly through dielectric and switching measurements. Large dielectric relaxation, which cannot be explained by dipole fluctuations of individual chain molecules around their axes, was observed in the dye-doped copolymer films. With increasing dye content in copolymers, the relaxation times increase, and the dielectric relaxation strength becomes large. However, the switching times and the switching curve are nearly independent of dye content. These results can be explained if we assume that dye is doped into noncrystalline regions but not into crystalline regions, and forms a long and slender phase boundary in which the dye content is high.