Donor-acceptor initiators, onium butyltliphenylborates (DPIB, DMPSB) containing both an onium cation (electron-accepting radical generator) and a berate anion (electron-donating radical generator) within the same compound were able to be sensitized by two aromatic ketones (2-chlorothioxanthone and Michler＇s ketone) to initiate polymerization of tetrahydrofurfuryl acrylate monomer. The photopolymerization efficiency of the onium butyltriphenylborates was higher than that of the onium salts (DPI, DMPS) or the berate compound (TBAB). The photoinitiation processes between the photosensitizers and the initiators have been investigated by laser flash photolysis. It has been clarified that two kinds of radical species are generated by a photoinduced electron-transfer mechanism.