Abstract: Silybin is an active principle of Silybum marianum (L.) Caertn,. this constituent possesses liver-protecting effect. In this experiment, ultraviolet spectrophotometric and double wave length thin layer scanning methods are used to determine the contents of silybin,water-soluble derivatives (silybin-N-methylglucamine, silybin phthalic acid mono ester sodium salt) and their preparations. It has been studied by controlling with the pure silybin isolated from the fruits of same species which was introduced from West Germany. Both of these two methods have been successfully investigated. The former can be used for the determination of crude drug, silybin derivatives and their preparations, while the latter is suitable for microanalysis.