A unique advantage of high voltage electron microscopy is the fact that continuous observation of phenomena by a variety of electron microscopy techniques is possible simultaneously with the introduction of point defect. Taking this advantage, fundamental studies to clarify the conditions under which non-equilibrium solid phases can successfully be produced under MeV electron irradiation have been undertaken. In this paper, three of the studies have been reviewed: one is concerned with the electron-irradiation-induced amorphization, the second the electron-irradiation-induced phase decomposition and the last the electron-irradiation-induced foreign-atom implantation.