At present, the treatment of the radiation-induced diseases are only performing by the palliative treatment technique. Moreover, radioprotective drugs are a little toxic for human being and this seriously limits their application with various complication in clinical uses. Accordingly, new radioprotectors need developing. In our Lab., we synthesized trithioformaldehyde (TTFA), containing three sulfur atom, and examined the effect on mouse jejunal crypt cells after irradiation. Mice treated with TTF A (2.0 g/ kg) showed 78% survival ratio at 30 day after 800 rad irradiation. 1.0 g/kg and 2.0 g/kg of TTF A increased resistance of jejunal crypt cells to single doses of radiation by protection factors of 1.17 and 1.23, respectively.