Abstract: Twelve thioxanthone derivatives were used for photosensitizing the gelation of poly vinyl cinnamate.It was shown that 2,4-Diisopropyl thioxanthone (DITX) and several others possess excellent photosensitizing power,the relative sensitivities being on the same level as 5-nitroacenaphthene.when the system of polyvinyl cinnamate-DITX (100:5) were exposed to the chemical fluorescent lamp (black lamp 360),the minimum quantity of exposure energy required for gelation of the polymer is about 5mj/cm².The mechanism of photosensitization and photogelation was also studied.It is likely that the mechanism is of the class of photocrosslinking process of dipolyme-rization due to energy-transfer from triplet state-DITXto ground state-polyvinyl cinnamate.