Introduction: Dental caries is a multifactorial disease that causes demineralization of the teeth. One of the main bacteria causing dental caries is Streptococcus mutans. Various natural antibacterial materials from plant extract can be used as an attempt to inhibit the growth of Streptococcus mutans and it has minimal side effects, one of which is butterfly pea extract. From the research that has been done, butterfly pea extract contains phytochemical compounds such as alkaloid, flavonoid, tannin, saponin, and ternatin which act as antibacterial agents against the growth of microorganisms. Objective: To prove that butterfly pea extract has potential as an antibacterial agent that can be observed from the formation of the inhibition zone of Streptococcus mutans. Methods: The in vitro study was conducted by diffusion method using 12 test groups with 4 times repetitions. The test group consisted of a positive control group with chlorhexidine 0.2%, a treatment group with 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% concentration of butterfly pea extract, and a negative control group with sterile distilled water. The samples were then incubated at 37ºC under anaerobic conditions for 24 hours. The inhibition zone formed was then measured using a caliper in millimeters (mm). Results: Butterfly pea extract can inhibit the growth of Streptococcus mutans starting at a concentration of 50%. One Way ANOVA test results P=0.001 (P<0.05), means that there are differences in the inhibition zone of Streptococcus mutans in each group. Conclusion: Butterfly pea extract can inhibit the growth of Streptococcus mutans.