The study was aimed at understanding behaviors of epoxy resins under electron beam irradiation, Epoxy resins of different molecular structures, which include glycidyl ether resin, glycidyl ester resin, glycidyl amine resin, and alicyclic epoxy resin, were irradiated with 5MeV electron beams. The irradiated samples were investigated with their viscosity changes, weight losses and gaseous molecules generated by the irradiation. The results show that the glycidyl ester resin and the epoxy containing ester group underwent the most serious decomposition bt the irradiation, while the glycidyl amine resin was decomposed less seriously and the glycidyl ether resin was the least decomposed.