Abstract: Yang-Jin-Hua(Datura)are toxic Chinese traditional drugs.It is found that there are 3 kinds of darura on the marker.In this paper,a quanti- tative method(by spectrophotometer)for determination of their toxic cons- tituents——two kinds of alkaloids(hyposcine and atropine)on two species of Yang-Jin-Hua(Datura innoxia Mill and D.stramonium L.)is described. Our study shows:1)The proportion of atropine in alkaloids is:flower- 79.9％,fruit-83.0％ and seed-84.7％;2)The proportion of hyoscine in alk- aloids is:flower-20.1％,fruit-17.0％ and seed-15.3％;3)The proportion of alkaloids in drugs is:flower-0.5389％,fruit-0.1306％ and seed-0.2361％.