Abstract: A number of plants belonging to the families Valerianaceae, Cruciferae and Compositae have been used in Chinese medicine as Bai-jiang-cao. The drug called "Su-bai-jiang" derived from the Cruciferous plant Thlaspi arvensis L. has been recorded in the Chinese Pharmacopoeia (1977 edition) under the name "Herba Thlaspis" and is widely used in eastern and southern China as the main source of Bai-jiang-cao.In this paper, the morphological and histological characters of this drug including the fruit, seed and stem are described in detail and illustrated with linedrawings.