The present invention provides new uses and products for treatment of diseases and disease conditions. More particularly, the present invention relates to the new uses of bioactive constituents derived from the said herb for the treatments of cancers. Additionally, the invention relates the methods and processes of applying the said bioactive constituents into the said treatments. There are disclosed bioactive polar organic constituents of Eurycoma longifo/ia Jack for the treatments of cancer. The said bioactive constituents comprise quassinoids and alkaloid wherein said quassinoids are eurycomanone and 13(21)-epoxyeurycomanone, and said alkaloid is 9-methoxycanthine-6-one, including all their respective analogues and derivatives of the said bioactive constituents. These bioactive constituents are used to irreversibly inhibit cancer cells growth and reduce the clonogenic capacities of the cancer cells at noncytotoxic concentrations, enhance the tumor suppressor activities, suppress the expression of cancer markers, suppress the expression of cancer-related genes, and modify the expression of genes associated with the controls of cell growth and functions. The overall discussed facts above indicate that the three Eurycoma longifolia Jack- derived bioactive compounds demonstrate anti-cancer properties, therefore, characterized as anti-cancer compounds.