Radiation-induced solid-state polymerization of acrylonitrile at low temperature is reported. It is pointed out that the rate of polymerization may be extremely rapid in the initial stage of polymerization in comparison with those induced with other radiation sources, that the effect of fast neutrons is significant in the polymerization, and that formation of both trans-vinylene and C˭C bonds conjugated with C≡N groups can be observed only in polymerization initiated with reactor radiation.