B Background: Periodontitis is an inflammatory disease of the gingiva (gingivitis)that is not treated. The bacteria that cause periodontitis are Gram negative bacteriasuch as Treponema denticola. The main treatment of periodontal disease is theelimination of bacteria through plaque control programs. Treatment of periodontaldisease can be done by non-surgical methods such as scaling, plaque control,antibacterial mouthwash, and systemic antibiotics. Cinnamon (Cinnamomumzeylanicum) is proven to contain compounds that are antibacterial. Purpose: toknowing the effectiveness of cinnamon extract as an antibacterial againstTreponema denticola. Method: This research is an in vitro experimental studyusing the microdilution method. Treponema denticola was cultured for 1 x 24 hoursthen given cinnamon extract with concentrations (100%, 50%, 25%, 12.5%, 6.25%,3.125%) BHI-B as a negative control and 0,2% chlorhexidine as a positive control.The antibacterial test was obtained by counting the total bacterial colonies obtainedby using the formula for the average total colony of bacterial colonies. The dataobtained were analyzed using the normality test, one-way ANOVA test, and ThePost-Hoc LSD test. Results: In the test of cinnamon extract against Treponemadenticola, minimum inhibitory concentration (MIC) was obtained at aconcentration 3.125% and minimum bactericidal concentration (MBC) at aconcentration 100%. Conclusion: Cinnamon extract is effective as an antibacterialagainst Treponema denticola.