Thiophene was polymerized by means of UVirradiation using diphenyliodonium hexafluorophosphate as a photoinitiator. An initiation mechanism involving electron transfer from photochemically generated onium radical cations to thiophene was proposed. N-Ethoxy-2-methylpyridinium hexafluorophosphate and triphenylsulfonium hexafluorophosphate were also found to be effective in facilitating the polymerization of thiophene. Polymerization is accompanied with the film formation on the surface of the reaction tube. The photochemically obtained polymers were characterized by FT-IR, DSC, and SEM analyses and compared with those obtained by oxidative and electrochemical means. Electrical conductivities of the samples were measured by four-probe technique.