Pineapple peel (Ananas comosus (L.) Meer) is the exhaust from the popular pineapple fruit consumed by many people. Pineaple peel contains enzyme bromealin and phenolic compound is tannins which can be used to inhibit the growth of Streptococcus mutans . The purpose of this study was to determine the antibacterial effectiv of gargle of ethanol extract of pineappele peel skin at activity against Streptococcus mutans, the effect of different concentrations of pineapple skin extract in inhibiting the growth of Streptococcus mutans and determine the concentration of pineapple skin extract (Ananas comosus (L.) Meer) are the most effective in inhibiting the growth of Streptococcus mutans. This study was an experimental study using post test only control group design. Pineapple peel extract made using maceration extraction method. The method used in the inhibition test using disc diffusion with 3 samples for each treatment. Sample consisted of seven treatment groups which is pineapple peel extract with concentration of 50%, 40%, 30%, 20%,10% , positive control group betadine mouthwash and negative control group (aquadest), data were analyzed using Descriptive. The results of this research showed pineapple peel extract concentration of 50%, 40%, 30%, 20% and positive control group betadine mouthwash had inhibition zone with strong category while consentrad 10% had moderate inhibitory zone category. The conclusion of this study prove that the pineapple peel extract has antibacterial activity against Streptococcus mutans with effective concentration of pineapple peel extract 20% , where the greater the concentration of the extract the greater the inhibition of growth of Streptococcus mutans.