B ackground: The prevalence of dental caries in Indonesia according to theRISKESDAS 2018 data are 88.8%. Streptococcus mutans is the main bacteriumthat causes dental caries. One way to prevent dental caries is to inhibit bacterialgrowth. Plectranthus amboinicus leaves contain compounds such as flavonoids,tannins, and saponins that have the ability to inhibit bacterial growth. Objective:To determine the effect of P. amboinicus leaf extract in inhibiting the growth of S.mutans. Methods: The agar media that had been inoculated by bacteria were placeda disc paper that had been soaked for 5 seconds in P. amboinicus leaf extract bothethyl acetate and hexane fractions with concentrations of 25%, 50%, and 75%. Thesame thing is done in distilled water, tetracycline, and chlorhexidine. Then,incubation was carried out for 24 hours and calculated the inhibitory zone formed.Qualitative phytochemical tests were carried out on P. amboinicus leaves by colorvisualization analysis techniques. Results: P. amboinicus leaf extract of ethylacetate fraction at 24 hours incubation with concentrations of 25%, 50%, and 75%resulted in inhibition zones of 3,8 ± 0,7 mm, 6,1 ± 0,8 mm and 7 ± 1,2 mm.Meanwhile, the hexane fraction with the same concentration after incubation for 24hours produced an average of 4,8 ± 0,8 mm, 6.6 ± 0,5 mm and 5.7 ± 1,1 mm. Inphytochemical tests using color visualization, the compound components containedin the leaves of P. amboinicus are flavonoids, tannins, saponins, and steroids.Conclusion: P. amboinicus leaf extract can inhibit the growth of S. mutans.