A novel phenacyl anilinium salt, N-phenacyl, NN-dimethylanilinium hexafluoroantimonate, (PDA), has been synthesized and used as photoinitiator for cationic polymerization of cyclohexene oxide (CHO), butyl vinyl ether (BVE) and N-vinyl carbazol (NVC). Plausible mechanism of the photoinitiation involves the decay of the excited PDA with both heterolytic and homolytic cleavages of carbon-nitrogen bond. Thus, phenacylium cations formed directly or subsequent intermolecular electron transfer, respectively, initiate the polymerization.