Epoxy resins have already been applied in electron beam (EB) curable composites structures extensively. The effects of different initiators and diluents on Shell Epon 828 radiation reaction were discussed in the paper, and the same radiation reaction systems were also explored using a heat treatment. The experimental results indicated cationic photoinitiator can initiate EB radiation curing of epoxy resin and traditionally heat-cured systems are not always suitable for the EB curing. The use of diluents would reduce the curing degree of resin and reactive diluents have less effect. The cationic ring-opening polymerization process including the decomposition of diaryliodonium salts under EB radiation at the initial stage and production of protonic acid that can initiate polyreaction was validated in the experiments. The characteristic of cured field and penetration process of EB in Shell Epon 828 system was also studied, and the whole cured area was found to be consisting of many lamellar structures. (C) 2002 Elsevier Science B.V. All rights reserved.