Marianine, the new lanostane triterpene (1) and marianosides A (2) and B (3) have been isolated from the whole plant of Silybum marianum. Their structures were elucidated on the basis of extensive analysis of their one dimensional and two dimensional nuclear magnetic resonance (1D, 2D-NMR) spectral data. All inhibited chymotrypsin in a concentration-dependent manner.