Propolis is a natural beehive product and its main constituents are polyphenolic compound, such as flavonoids and cinnamic acid derivatives. Objectives: To investigate in vitro antimicrobial activity of Propolis on Streptoccoccus mutans. Methods: Propolis from Parung Panjang West of Java Indonesia was examined for bacterial growth inhibition by determining the inhibitory zone (agar diffusion method), minimum inhibitory (MIC), and minimum bactericidal concentration (MBC). The microorganisms tested were: Local strains of Streptococcus mutans isolated from school children harbouring such species in Bangka Island Indonesia labeled as: S. mutans 1, S. mutans 2, S. mutans 3, S. mutans 4, S. mutans 5 and S. mutans 6. The concentration of Propolis polyphenolic compound used 62.5ug/ml Propolis polyphenolic. Results: The MIC value were 31.25ug/ml, average of inhibition zone 2.125 mm for S.mutans1; 31.25ug/ml, 3.57mm for S. mutans 2; 31.25ug/ml, 2.00 mm for S. mutans 3; 31.25ug/ml, 2.80 mm for S. mutans 4; 31.25ug/ml,2.60 mm for S. mutans 5; 31.25ug/ml,2.45 mm for S. mutans 6. Their MBC values were two times higher than MIC. Conclusion: This study shows that Propolis polyphenolic compund has antimicrobial activity against local strains of Streptococcus mutans isolated from school children.