Garcinia mangostana has been documented in Thai traditional medicine in various aspects. Although many benefits have been claimed, few scientific reports are available in the literature. In the present study, the methanolic extract from G. mangostana hulls (GME) was assessed for antioxidant and cytoprotective activities. The results showed that GME contained phenolic compounds and possessed reducing power as well as Fe 2+ chelating activity. The antioxidant properties were determined by scavenging DPPH, nitric oxide and lipid radicals in dose-dependent manners. In particular, the powerful scavenging activities were found against hydroxyl and superoxide radicals when investigated using ESR spectrometry. GME also enhanced the cell survival by decreasing the oxidative damage in ECV304 endothelial cells after H 2 O 2 exposure. These data indicated that GME played a pivotal role on the antioxidant and chemopreventive activities via a reducing mechanism and inhibition of intracellular oxidative stress, respectively.