The radiation-induced polymerization of zinc chloride-acrylonitrile (AN) complexes, both the amorphous ZnCl2-AN (1:l) type and the crystalline (1:2) type, was carried out at 30 and -35°C. The rate of polymerization of the 1:1 type exceeds that of the 1:2 type not only in bulk but also in their benzene (BZ) solution, which seems to be attributable to the difference in the relative concentration of ZnCl2to AN rather than to difference in their phases. The addition of a small amount of water to both type complexes results in an increase in the rate of polymerization. In the BZ solution of the 1:2 type complex (Zncl2:AN:BZ = 1:2:2), the addition of water, methanol, and acetic acid increases the rate of polymerization, and the apparent G value of initiation increases with the added amount of water. The findings indicate considerable contribution of the added ligands coordinated to zinc cation to formation of initiating species on irradiation. The bromine atom number NBrper polymer chain was measured by means of radioactivation analysis for polymers obtained from the polymerization of ZnBr2-AN complexes. NBrof 0.20 for both 1:1 and 1:2 types suggests a minor contribution of the initiation by addition of the bromine radical to monomer molecules. In the BZ solution of complexes of the 1:2 type, the NBrof 0.19 was reduced to 0.13 upon addition of water (0.2 mole ratio), which indicates some contribution of water to formation of initiating species. The result is in accord with the estimation based on the rate increase.