M Mahkota dewa (Phaleria macrocarpa) is a typically popular Indonesian fruit that can be used as an alternative in controlling some diseases. The fruit contains one of an active component, flavonoid, which can be beneficial as an antibacterial compound. Periodontal disease is an inflammation result of bacteria infection on periodontium. The etiology of this disease is bacteria accumulation that colonizing, binding, attached on the tooth surface, and be shrouded by an organic polymeric substance (EPS), which is called biofilm. One of the negative-Gram bacteria that commonly create a biofilm formation is Treponema denticola. The aim of this research is to examine the effect of mahkota dewa fruit extract on the viability of Treponema denticola biofilm. Mahkota dewa was crushed into powder, dissolved using ethanol and was evaporated to be an extract. Mahkota dewa fruit extract was diluted into concentrations of 25%, 12,5%, 6,25%, 3,125%, and 1,56% by using a sterile aquades. Treponema denticola were cultured on BHI-B. The result of bacteria cultured were distributed into the 96-well microplate, which was coated earlier with saliva, and incubated. Subsequently, a different concentrations of mahkota dewa fruit extract were distributed in biofilm containing well and incubated for 1, 6, and 24 hours. The measurement of biofilm inhibition can be shown by microplate reader in optical density (OD). The result has shown that mahkota dewa fruit extracts were effectively inhibit the viability of Treponema denticola biofilm at the concentration of 1,56% in 1 hour (OD 0.80 ± 0.03), the concentration of 25% in 6 hours (OD 2.37 ± 0.01), and the concentration of 25% in 24 hours (OD 1.28 ± 0.06). Based on the research, it can be concluded that mahkota dewa fruit extract can inhibit Treponema denticola biofilm.