Three new xanthones were isolated from the bark of Garcinia dioica (Guttiferae) in addition to a known xanthone, 1, 3, 6-trihydroxy-8-geranyl-7-methoxyxanthone (rubraxanthone). The structures of the three xanthones were elucidated to be 1, 3, 6-trihydroxy-8-(7-hydroxy-3, 7-dimethyl-2, 5-octadieyl)-7-methoxyxanthone, 1, 3, 6-trihydroxy-8-(6, 7-epoxy-3, 7-dimethyl-2-octenyl)-7-methoxyxanthone and 1, 3, 7-trihydroxy-2, 4-diisoprenylxanthone by the aid of spectroscopic analysis including the two dimensional NMR technique. The occurrence of xanthone with such a C₁₀ alkyl chain is rare in naturally occurring compounds.