Silibinin is a major component of silymarin (Silybum marianum) which has traditionally been used to treat a wide range of liver diseases. Recently Silibinin and its derivatives in both in vitro and in vivo models have shown a significant inhibitory effect in different types of tumors including skin breast lung colon bladder prostate kidney and liver. The chemo-preventive potentials of this flavonoid are promoted by inducing apoptosis enhancing tumor suppressor and cell cycle inhibitors inhibiting growth factors and attenuating proliferative mediators. In this paper a summary of the important molecular mechanisms involved in Silibinin anti-cancer effects animal studies and important clinical trials have been presented. The results of these studies will provide a more comprehensive perspective of Silibinin and help to optimize its effects in cancer chemotherapy.