Chronic Lymphocytic Leukemia (CLL) is the most common type of leukemia in western countries. One of the most important strategies in CLL chemotherapy is apoptosis induction in CLL cells. Over the last decades herbal medicines and their constituents attract the attentions for chemotherapy of CLL. Umbelliprenin is a sesquiterpene coumarin, that is synthesized by various Ferula species. Apoptosis induction and cytotoxicity toward cancerous cells by umbelliprenin, firstly showed in 2008. In my Ph.D thesis I studied the properties of apoptosis induction in CLL cell lines by umbelliprenin. For the first time I should that umbelliprenin could induce apoptosis in CLL cell lines time- and dose- dependently. umbelliprenin and other natural coumarins are hopeful compounds in the future of CLL chemotherapy.