Hydrogen retention property on isotropic graphite was studied by exposure with a high flux atomized D/T particles. From the analysis of thermal desorption spectra it is clarified that deuterium implanted to graphite existed in two different states, one was that in a trap site the other was that of C-D bond. The amount of deuterium retained in graphite was in proportion to a half power of total incident fluence and no saturation was observed up to 1026 atoms·m−2. The total hydrogen isotope retention in the sample exposed to atomized D/T particles with total incident fluence of 1025 – 1026 atoms·m−2 were in the range of 1 × 1022−4 × 1022 atoms·m−2.1Visiting researcher from Toshiba Co.