Dental and oral diseases often experienced by Indonesian are dental caries and mouth ulcer. Streptococcus mutants often cause dental caries, and the fungus that causes mouth ulcer is Candida albicans. Suppose dental caries and mouth ulcer are not resolved immediately. In that case, it can be fatal because the nervous system and blood vessels connect throughout the body, so the bacteria can cause infections in vital organs such as the heart, kidney, and brain. One example of a plant with antibacterial abilities is mint leaves (Mentha piperita) because it has terpenoid compounds, especially menthol. This study aimed to determine the effect of gargling using a decoction of mint leaves on bacteria in dental caries and Candida albicans on mouth ulcer. The type of studied was experimental, with a sample of 25 respondents divided into the five treatment groups, namely the positive control group (povidone-iodine 1%) and negative control (mineral water), the gargle treatment group concentration of decoction of mint leaves on 10% (P1), 20% (P2), and 30% (P3). Data analysis using Paired Sample T-Test test with a significance level of 95% and statistical program SPSS 16.0. The results showed that rinsing the mouth using mint leaves at 10%, 20%, and 30% reduced bacterial colonies in dental caries and Candida albicans on mouth ulcer. Decoction of mint leaves used for rinsing the mouth with a concentration of 20% has the best effect in reducing the number of bacterial colonies in dental caries (p<0.05).