RESUMEN
<p><b>OBJECTIVE</b>Study on the antibacterial activity of Viola yedoensis and the antibacterial active compounds.</p><p><b>METHOD</b>The chemical compositions were isolated by means of solvent extraction, column chromatography on silica gel, sephadex LH-20 and crystallization. The antibacterial activities were tested by Neo-Sensitab disk-diffusion method, nephelometric analysis and plating method.</p><p><b>RESULT</b>One new compound (4) along with three known compounds were isolated from this plant for the first time and were identified as aesculetin (1), 6,7-dimethoxycoumarin (2), scopoletin (3) and 5-methoxy-7-hydroxymethylcoumarin (4), respectively. All the compounds showed antibacterial and antibactericidal activities at varying degree on Streptococcus Aureas, S. agalactiae, S. uberis, S. dysgalactiae, E. coli and Salmonella, of which 1 was most active with 0.031- 0.313 g x L(-1) of minimal inhibitory concentrations (MIC) and 0.313 - 0.625 g x L(-1) of minimal bactericidal concentrations (MBC).</p><p><b>CONCLUSION</b>Viola yedoensis has a broad spectrum of antibacterial activity on animal pathogenic bacteria, and coumarins may be the main antibacterial activity ingredients.</p>