Has done research on the effectiveness of the test preparation of the ethanol extract mouthwash Leaf Prasman (Eupatorium triplinerve Vahl.) against Streptococcus mutans. This study aims to determine the effectiveness of the ethanol extract siwak tree on the growth of Streptococcus mutans bacteria. The method used in making the extract by using methods maserasi. The extract is then formulated with various concentration of 1%, 2% and 4%, and control without active substance. Tests conducted mouthwash among other organoleptic testing, pH and antimicrobial activity test performed using the agar diffusion method to determine the diameter of barriers against Streptococcus mutans using piperdisk on Medium Nutrient agar (NA). After a 24 hour incubation zone of inhibition obtained at a concentration of 4%, 2%,dan 1% is equal to 11.66 mm, 10.5 mm, and 9.01 mm and for the control formula of 7 mm. This suggests that higher concentrations 4% provide better power resistor.