ABSTRACT A new alkaloid, 2-butoxy-3-chloropyrazine (P1) together with Supinine (P2) and Indicine (P3) were isolated from the ethyl acetate extract of the roots of Asteropeia densiflora BAKER (ASTEROPEIACEAE) an endemic plant of Madagascar. This plant is applied by villagers as timber and by woodworkers as a fortifier. The use of chromatographic technique allowed the isolation of the three alkaloids. The structures of these secondary metabolites were established using detailed spectroscopic analysis and by comparison with published data. These antibacterial activities of the ethyl acetate extract was evaluated by Agar diffusion tests. Antibacterial tests have shown that the extract inhibit the strains of Bacillus subtilis, Staphylococcus, Streptomyces viridochromogenes, and Escherichia coli. The chemical and biological results indicate that Asteropeia densiflora contains bioactive molecules like other studied species of this genus. KEYWORDS: Asteropeia densiflora, 2, 3-disubstituted pyrazine, antimicrobial.