Abstract: The root of Rei—Xiang—Lang—Du (Stellera chamaejasme L.) is recognised to be tosic and therefore will be identified when it is necessary in criminal case. But how to identify it is a problem. Hence in order to solve, if possible, this problem, a general description of the morphological and histological characters of the root will be made and the chemical analysis will be studied. In this paper, how to apply the method above-mentioned into the identification of decocted dregs was discussed.