The water-solution photo-polymerization of acrylonitrile in inorganic salt such as NaSCN, KSCN, NH₄SCN, Ba(SCN)₂, ZnC1₂ which is being used as solvent for acrylic fiber production was studied. Under irradiation of high-pressure mercury lamp(365nm), acrylonitrile was polymerized to higher conversion and molecular weight without the addition of any additional initiator(sensitizer). Overall activation energy was 1.33 kcal/mol.