Abstract: A recent survey showed that the crude drugs under the name "Hou-pu" are derived from the genera Magnolia (including 11 species) and Manglietia (4 species), belonging to the Fam. Magnoliaceae. According to their origins and qualities, they can be classified into four kinds: viz. 1. Hou-pu (厚朴类), 2. Jiang-pu (姜朴类), 3. Zhi-zi-pi (枝子皮类) and 4. Tu-hou-pu (土厚朴类) (cf Tab 1).Owing to compounds Ⅰ, Ⅱ and Ⅲ are the main active constituents in Magnolia offieinalis, all 15 species (cf Tab 1) were examined for these compounds by means of IR, UV and TLC. The result revealed that Ⅰ, Ⅱ and Ⅲ are highly concentrated within the "Hou-pu" kind of drugs. Systematically, they are all derived from plants belonging to the Gen. Magnolia Subgen. Magnolia Sect. Rytidospermum, including M. offieinalis, M. biloba and M. rostrata etc, in which contents of Ⅰ and Ⅱ are higher (more than 1%). It was demonstrated that M. officinalis and M. biloba should be regarded as the genuine "Hou-pu".Since the second kind Zhi-zi-pi derived from the Sect. Oyama and the third kind Jian-pu derived from the Subgen. Pleurochasma Sect. Yulania, Tulipastrum and Buergera contain no Ⅰ, Ⅱ, Ⅲ or merely a very small amount, they may be all treated as adulterants.The fourth kind Tu-hou-pu originating from Gen. Mangleitia, however, contain compounds Ⅰ and Ⅱ. It is, therfore, noteworthy for further research as a new resource.Consequently, the presence of compounds Ⅰ, Ⅱ and Ⅲ may be used as a Criterion for evaluation of the quality on "Hou-pu".