The cytotoxic activities and antitumor properties of xanthones are evaluated using bioassay methods. To quantitatively compare the cytotoxic potency of the tested compounds, four parameters are calculated which include GI50, IC50, TGI, and LC50. GI50 is the concentration of the anti-cancer drug that inhibits the growth of cancer cells by 50%. In other words, after giving the drug, there is a 50% reduction in cancer cell proliferation. IC50 is the concentration of a drug that inhibits a biological activity by 50%. Besides GI50 and IC50, TGI also be one of parameters which is the concentration of test drug and it also signifies cytostatic effect. Differ from TGI; LC50 is Lethal Concentration 50, which signifies cytotoxic effect. In other words, LC50 is the concentration in water having 50% chance of causing death to aquatic life