Photoirradiation of fluoropolymer films in contact with an aqueous solution of sodium sulfite made the surface hydrophilic. After ion exchange with concentrated sulfuric acid, the surface showed a high acidity and induced the cationic polymerization of N-vinylcarbazole, which is based on the presence of sulfonic acid groups on the fluoropolymer chain. It is strongly suggested that the reaction proceeds in an electron transfer mechanism where fluoropolymer is activated by the capture of a hydrated electron photochemically released from sulfite ion (SO32-).