The isolation and identification of an antibacterial component, from the leaves of Liriodendron tulipifera. K. Kotch against a cariogenic bacterium Streptococcus mutans OMZ 176, were carried out for developing of anticariogenic agents. The bioactive component was elucidated as ${eta}-liriodenolide$, which was isolated newly from the leaves of L. tulipifera. The minimal inhibitory concentration (MIC) of ${eta}-liriodenolide$ was $100;{mu}g/ml$ and the antibacterial activity was stronger than that of berberine. ${eta}-Liriodenolide$ inhibited ${eta}-lactamase$ activity, 50, 100 and $200;{mu}M$ ${eta}-liriodenolide$ did ${eta}-lactamase$ activity as 0.7, 3.5 and 19.7%, respectively. The toxicity of ${eta}-liriodenolide$ was not found with the method of photohemolysis.