Methanolic extracts of 14 plant species used in traditional medicine in Madagascar were investigated for their antibacterial activities. Several extracts showed high inhibitory activities (Maytenus polyacantha, Mystroxylon aethiopicum, Psychotria bridsoniae, Dombeya tsaratananensis, Psychotria oreotrephes, Razafimandimbisonia sambiranensis) against Listeria monocytogenes, Staphylococcus aureus and Streptococcus pyogenes strains, some of which reached a MIC value lower than 0.1 mg/ml. The extract of P. oreotrephes was the most active against Clostridium perfringens, Proteus mirabilis and Yersinia enterocolitica. Escherichia coli and Salmonella Enteritidis were resistant to all tested extracts. This study demonstrates that plant extracts from species belonging to the Lauraceae, Proteaceae, Celastraceae, Malvaceae and Rubiaceae families have high antibacterial activity, some of which are bactericidal, against Gram-positive pathogenic bacteria that are known to cause infectious diseases.