The composition and the antimicrobial activity of the bark oil of Santiria trimera (Oliv.) Aubrév., a plant widely used by the traditional healers in S. Tomé and Príncipe, especially for wound healing, are reported for the first time. The analysis of the essential oil was carried out by GC and GC-MS. The oil contains a high content of monoterpenes, alpha-pinene (66.6 %) being the major constituent, followed by beta-pinene (20.0 %). The essential oil was active against both bacteria and fungi strains, except Staphylococcus epidermidis and Aspergillus niger. It exhibited significant antimicrobial activity against Proteus vulgaris and Cryptococcus neoformans with MICs values of 1.11 microl/ml and lower than 0.71 microl/ml, respectively.