METHODS AND RESULTS: Three xanthone derivatives, gambogic acid, Isogambogic acid and isomorellinol, were isolated from the dried latex of Garcinia hanburyi. Two of them, Isogambogic acid and isomorellinol, are new. Determinations of the structures and stereochemistry were achieved independently by a series of NMR experiments including COSY, ROESY, HMQC, HMBC and selective INEPT. Isolation of isomorellinol from G. hanburyi provided important chemical evidence to link this species to G. morella. The presence of gambogic acid and Isogambogic acid, however, demonstrated the difference between these two species. CONCLUSIONS: Cytotoxic evaluation of these isolates revealed that all three were active against KB and drug-resistant KB-V1 cell lines.