To evaluate the effect of eucalyptus, sappan, and cinnamon leaf and bark extract on the percentage of S. mutans biofilm formation. The test group was divided into a negative control (1% Dimethyl sulfoxide), a treatment group (eucalyptus, sappan, and cinnamon leaves and bark at concentrations of 50%, 25%, and 12.5%, respectively), and a positive control (0.2% chlorhexidine). Each concentration of eucalyptus, sappan, and cinnamon leaves and barks extract, Brain Heart Infusion Broth (BHI-B), bacteria according to the McFarland 0.5 standard, a positive control, and a negative control were added to a 96-well microplate. They were incubated at 37 °C for twenty-four hours before being rinsed with phosphate buffer saline (PBS) and stained with 0.1% crystal violet. The optical density was then measured using a microplate reader with a 540 nm wavelength. The absorbance value is then factored into the percentage of bacterial adhesion inhibition formula. A statistical test revealed a significant difference (p < 0.05) in the percentage of inhibition between the three extracts of leaves and bark and the negative control group (1% DMSO). There is a significant difference between all leaves and barks concentration and the positive control group except the 50% concentration of sappan leaf group and 50% concentration of cinnamon leaf group. The sappan leaf and cinnamon leaf at 50% concentration exhibit no significant difference (p > 0.05) with the positive control. Eucalyptus, sappan, cinnamon leaves and barks at a concentration of 50% demonstrated effectiveness of the extractant in inhibiting the formation of biofilm masses by S. mutans in comparison with the other group.