Abstract: These years, with the rapid development of radiation therapy and intense situation of the worldwide nuclear security, radioprotective agents have caused wide concern again, especially after Fukushima nuclear accident. Application of drugs is one of the most useful and direct methods to prevent radiation damage, and will lead to attenuated body injuries before exposure to rays. Even after exposure, the radioprotectant application will also result in alleviated clinical symptoms and rapid recovery. In 1949, Patt reported that acute radiation injury could be prevented by cysteine. Now, over half a century has elapsed. Numerous detailed studies on drugs aiming at preventing radiation damage have been conducted by many countries. This paper was written for introducing the brief history of research on radioprotective agents, classification and mechanism of action, of course, prospect involved as well.