Abstract: The drug Wu-Chiu-Keng described in Pen-Tsao-Kang-Mu, the Chinese Materia Medica, as purgative and hydragogue has been used as diuretic in China for centuries. It is reported recently that this drug is effective against Schitosomiasis Japonicum. In view of the fact that so far no information regarding its chemical constituent has been reported, the present investigation was undertaken. The material for this experiment was obtained from Ningko district, Anhui province. A crystalline substance melting at 80--81℃ was isolated and its molecular formula was determined to be C₁₀H₁₂O₄. According to its chemical and physical properties it was identified to be xanthoxylin.