Abstract: A copolymer comprising (a) a monomer having a C.sub.7 to C.sub.21 perfluoroalkyl or perfluoroalkenyl group at one end of the molecule and an ethylenically unsaturated group at the other end of the molecule, and (b) a monomer having a photosensitive group, e.g. an azidobenzoyloxy group, cinnamoyloxy group, benzoylphenyl group or .alpha.,.beta.-unsaturated ketone group. The copolymer has an excellent photosensitivity and excellent water and oil repellent properties, and is useful for various purposes, e.g. as a photosensitive material for dry offset printing plate or resist and as a photo-curable, water and oil repelling coating material.