In this annual report, the activities of education and research, the state of operation of research facilities and others in Nuclear Engineering Research Laboratory, University of Tokyo in fiscal year 1991 are summarized. In this Laboratory, there are four large research facilities, that is, the fast neutron source reactor `Yayoi`, the electron beam linac, the nuclear fusion reactor blanket experiment facility and the heavy irradiation research facility. Those are used for carrying out education and research in the wide fields of nuclear engineering, and are offered also for joint utilization. The results of the research by using respective research facilities were summarized in separate reports. In this annual report, the course of the management and operation of respective research facilities is described, and the research activities, the theses for doctorate and graduation theses of the teachers, personnel and graduate students in the Laboratory are summarized. In the research, those on first wall engineering for fusion reactors, fuel cycle engineering, electromagnetic structure engineering, AI and robotics, quantum beam engineering, new type reactor design and so on are included. (K.I.).