Primary processes of photoinduced cationic polymerization of α-methylstyrene in the presence of tetracyanobenzene or pyromellitic dianhydride have been investigated by the nanosecond laser photolysis method. Ionic photodissociations in both charge-transfer singlet and triplet states are observed for the α-methylstyrene-tetracyanobenzene complex in methylene chloride. The contribution of these two states to the ion yield was found to depend on the temperature. In the case of the α-methylstyrene-pyromellitic dianhydride complex, however, ions are formed exclusively from the charge-transfer triplet state. The decay behavior of ion pairs depends on the states from which they are formed. Ions formed from the singlet state decay faster than those from the triplet state. The difference was interpreted by the concept of spin conservation in the reaction system. Initiation processes, i.e., dimerization and trimerization, were also elucidated. The ions formed from the singlet state neither give a photocurrent nor do they initiate photopolymerization, while ions formed from the triplet state give a photocurrent and react with the monomer to form a dimer radical cation of α-methylstyrene. The dimerization rate constant was estimated to be 1 × 105 M-1 sec-1.