In its study, We investigated the effects of Areca catechu L on the growth and acid production of Streptococcus mutans JC-2 in broth system and the activity of glucosyltransferase. The results were summarized as follow; 1. The growth of Streptococcus mutans JC-2 was suppressed by adding Areca catechu L in broth system. Especially, its inhibitory effect was significant at 2,000ppm of concentration. 2. Areca catechu L decreased the acid production of Streptococcus mutans JC-2. Decrease of pH according to acid production was less in presence of Areca catechu L than in absence. 3. Areca catechu L exerted the inhibitory effect against glucosyltransferase activity form Streptococcus mutans JC-2.