SAR analysis revealed that the anti-proliferative activity of the xanthones is substantially influenced by the position and number of attached hydroxyl and prenyl groups, and the presence of hydroxyl group ortho to the carbonyl function of xanthone scaffold contributes significantly to their cytotoxicity. The new prenylatedxanthone 20 with a relatively simple structure, namely 1,3,8-trihydroxy-2-prenylxanthone