Ethnopharmacological relevance: Macaranga Thou. (Euphorbiaceae) is a large genus that comprises over 300 species distributed between Western Africa and the islands of the South Pacific. Plants of this genus have a long-standing history of use in traditional medicine for different purposes, including the treatment of inflammation. Fresh and dried leaves of certain Macaranga species (e.g. M. tanarius (L.) Müll.Arg.), have been used to treat cuts, bruises, boils, swellings, sores and covering of wounds in general. Several reports described Macaranga spp. being a rich source of polyphenols, such as prenylated stilbenoids and flavonoids, mostly responsible for its biological activity. Similarly, an abundant content of prenylated stilbenes was also described in M. siamensis S.J.Davies, species recently identified (2001) in Thailand. While the respective biological activity of the prenylated stilbenes from M. siamensis was poorly investigated to date, our recent study pointed out the interest as the natural source of several novel anti-inflammatory stilbenoids isolated from this species.