In order to find more effective radioprotective agents from cinnamic acid thioester derivatives, the structure ofP — hydroxycinnamic acid and sinapic acid into 4'— O —carbethoxy — 2— chlorocinnamic acid diethylaminoethylthiol estenrhydrochloride and 3, 4,5— trimethoxyphenylpropenoic acid diethylamino ethylthiol ester hydrochloride has been changed. The main step of synthesise of these agents involved the condensation of 4' — O —carbethoxy — phenylpropenoic acid chloride with diethylaminoethylthiol under base catalyst. The protective test on mice irradiated with ,60,Co γ-rays of 7.5~ 8.0Gy was shownthat the animal survival rate was enhanced by 30% within 30 days afterirradiation in comparision with the control group. The MS,IR and NMR spectra data of cinnamic acid thioester derivative have alsobeen reported. The ESR spectra of the compound was discussed.