P eriodontal disease is one of the most common oral health problems in the world. Poprhyromonas gingivalis is one of the three red complex bacteria that are pivotal in the pathogenesis of periodontal diseases. Prevention of periodontal diseases by plaque control can be facilitated by the use of herbal plants such as miswak (Salvadora persica) that has been used for thousands of years to clean teeth and mouth. Studies have shown that miswak has antibacterial effects against oral bacteria. This study aims to determine the effect of miswak extract on the density of Porphyromonas gingivalis biofilm in vitro. P. gingivalis was cultured in 3 well-plates for 3x24 hours. Different concentrations of miswak extract (100%, 50%, 25%, 12.5%, 6.25%, 3.12%, 1.5%, and 0.78%), Tryptic Soy Broth (negative control), and 0.2% chlorhexidine gluconate (positive control) were added and the well-plates were incubated for 1 hour, 6 hours, and 24 hours at 370C. Biofilms in the well-plates were stained using crystal violet and optical density was measured using a microplate reader. Measurement of optical density shows that every concentration of miswak extract inhibits the density of P. gingivalis biofilm. The extract concentration with the highest inhibition activity is 50% for the 1-hour and 6-hour incubation periods, and 25% for the 24-hour incubation period. Statistical analysis using one way-ANOVA shows that miswak extract inhibits the density of P. gingivalis biofilm (p<0.05). Post-Hoc analysis using Tukey shows that there is a significant difference between 50% miswak extract with 0.78% miswak extract and the negative control for the 1-hour incubation period. Data of the 6-hour incubation period shows that there is a significant difference between 100% to 0.78% miswak extract with the negative control and data of the 24-hour incubation period shows that there is a significant difference between 100% to 1.5% miswak extract with the negative control.