In order to investigate the mechanisms of radiation-induced grain boundary migration,a 316 model steel and Ni-(2-10)at%Si model alloys were electron-irradiated. Boundary migration was often observed in stainless steels and the model alloys during irradiation. An initial incubation and three migration stages were observed.The incubation period depended on irradiation temperature and solute concentration. From the temperature dependence of boundary migration velocity during the first stage and the incubation response, activation energies were estimated. The activation energies obtained for each alloy were lower than that for boundary migration under thermal annealing. It is suggested from these results that the grain boundary migration under irradiation is caused by enhanced boundary diffusion and preferential rearrangement of under sized interstitial solute atoms diffusing via a mixed dumbbell mechanism towards the grain boundary.