Abstract: The main active constituents——osthol and imperatorin were isolated from Cnidium monnieri (L.)Cuss and then used as standards for their determination in the crude drug by fluorometry TLCS.The fructus Cnidii was macerated with ethanol overnight and the ethanolic extract was spotted on a silica gel G-CMC Na plate. The plate was developecl with n-hexane-ethyl acetate (7:3). The spot was excited by light of 365 nm, and determined in a Shimadzu CS-930 TLC scanner using a No. 2 filter. The peak areas of the two components were obtained, external standard method was used in the determination.The root, stem,leaf and flower of this plantwere shown to contain no osthol and imperatorin, and the seed was found to contain 2.0～3.2% of osthol and 1.8～2.5% of imperatorin.