In this mini-review, the biological actions silymarin are reviewed. Milk thistle (Silybum marianum) is widely used in a traditional medicine. Silymarin, the active components of milk thistle, contains three isomers including silybin, silydianin and silychristine. Silybin is the most proportion and biologically the most active ingredient of silymarin. It possesses various properties including hepatoprotective, anti-cancer, anti-inflammatory, antioxidant, as well as hypocholesteromic activities.