Abstract: The dried barks of Melia toosendan S.et Z.(family Simarubaceae)produced in Szechuan province has long been used in Chinese medicine as an anthelmintic remedy.Its effectiveness against ascariasis has been proved by pharmacological and clinical investigations. However,this bark has been found sometimes to be substituted or grossly adulterated due to the ignorance of the collectors with the bark of Picrasma quassioides Benn. This paper gives detailed descriptions of the macroscopical and microscopical characters of the abovementioned barks.Their more important diagnostical features are listed in the following table: