The lipid peroxidation inhibitory activities of four hydroxyxanthones, isolated from the whole plant Swertia decussata, were evaluated for the first time. The most promising antioxidant among the xanthones, 1,7,8-trihydroxy-3-methoxyxanthone (swertianine,4) was also tested for its scavenging potential against DPPH and superoxide radicals. The data clearly revealed good antioxidant activity of the xanthones, especially 4 which also showed strong protection against -ray induced pBR322 DNA damage. A comparison of the radioprotecting activities of the monomethylated tetrahydroxyxanthone 4 with that of its congener, 1,3,7-trihydroxy-8-methoxyxanthone (5) revealed that the radioprotecting activity was not affected by the position of methylation