In view of the rapid increase of nuclear energy facilities such as power plants, fuel-reprocessing plants and so forth, the safe control of the disposal of radioactive wastes into the sea has been and will be of great concern in the world. The present paper deals with the following matters; (1) historical background information of radioactive contamination of the sea due to the past military use of atomic energy, (2) natural and artificial radioactivity in the sea, (3) general features of the behaviour of radioactive nuclides in marine environment, (4) safe management of coastal discharge of radioactive liquid wastes, (5) disposal of solid radioactive wastes into deep sea bottom, and (6) problem on international control of radioactivity release in marine environment.
