[en] The Tokai Reprocessing Plant (TRP) was designed for an annual reprocessing capacity of 210 tons of spent fuels with the average burn-up of 28,000 MWd/MTU as the first reprocessing plant for commercial light water reactor (LWR) power stations in Japan. The TRP had been processed over 1,100 tons of spent fuels since the beginning of the hot-test in 1977. Almost of radioactive materials in the liquid waste were removed out by the treatment process using multiple evaporators. The liquid effluents were discharged to the sea through a 3.7 km long pipeline after confirmation of concentration of radionuclides beneath the limits by the Safety Regulation of the TRP. Furthermore, the environmental monitoring had confirmed not to be caused an unexpected influence to the marine environment. The environmental monitoring for seawater, sea sediments and marine products such as fishes, shellfish and seaweeds had been carried out offshore the Tokai-mura since 1977. In 2006, the TRP finished reprocessing of spent fuels based on the contracts with domestic power companies in possession of nuclear power plants and changed the purpose of its operation to the investigation one. This report reviewed comprehensively the all data obtained marine environmental monitoring since 1977. (author)