Yam was stepwise extracted with hexane, chloroform, ethyl acetate, butanol, and water. Antibacterial activity of each extract was investigated. 1. Methanol extract of Yam was examed against to antibacterial effects on S. mutans KCTC 5316, P. gingivalis KCTC 5352, S. aureus KCTC 1927 by means of agar diffusion method. 2. The methanol extract of Yam was showed very powerfull antibacterial activity on S. mutans, but not showed on P. gingivalis, and S. aureus. 3. The MIC of Yam hexane fraction was 0.25 mg/ml for S. mutans KCTC 5316. 4. The Yam hexane fraction strong inhibited the growth of S. mutans, in the culture medium at concentration of 0.25 mg/ml.