Introduction: Caries is a chronic infection of tooth tissue which is experienced by 50% of the world's population. Loss of teeth due to caries can cause problems, including mastication disorders. Caries can occur due to the activity of the main bacteria, ie Streptococcus mutans (S. mutans). A solution is needed to inhibit the growth of S. mutans bacteria, one of them with montong durian peel extract (Durian zibethinus murray) which has antibacterial properties such as flavonoids, saponins, and tannins. Purpose: Proving the antibacterial potential of montong durian peel extract against growth barriers of Streptococcus mutans. Methods: This research is an in vitro study with a posttest only control group design. Montong durian peel extract was obtained by maceration method, and divided into concentrations of 90%, 45%, 22.5%, 11.25%, 5.625%; with replication of each concentration 6 times. The tests carried out included phytochemical tests, Minimum Inhibitory Concentration (MIC) tests and Minimum Bactericidal Concentration (MBC) tests. The data obtained was then tested statistically with ANOVA. Results: There was a significant difference between the groups for the MIC test (p = 0.00) and for the MBC test (p = 0.00), with MIC at a concentration of 22.5%, and MBC at a concentration of 45%. Conclusion: Montong durian peel extract has antibacterial potential that can inhibit growth of S.mutans.