Streptococcus viridans can cause subacute bacterial endocarditis in humans. Dentists should be cautious in root canal treatment. Irrigation is one of the stage in root canal treatment. The material usually used is sodium hypochlorite. Sodium hypochlorite could irritate the tissues. Alternative material is needed like cherry leaf (Muntingia calabura L.). Cherry leaf has an active content of flavonoids, saponins, and tanins as antibacterials. To determine antibacterial ability of cherry leaf extract againts Streptococcus viridans and to know the concentration of cherry leaf extract which has the biggest inhibition ability againts Streptococcus viridans. This research consist of 5 groups: possitive control (sodium hypochlorite), P1 (cherry leaf extract 12,5%), P2 (cherry leaf extract 25%), P3 (cherry leaf extract 50%), P4 (Cherry leaf extract 75%). BHI-A medium was planted with Streptococcus viridans suspension. Furthermore the disc paper that has been treated according to the group placed on the BHI-A medium. Medium Incubated for 24 hours, then the inhibition zone diameter measured. The largest inhibition zone was in the P4 group (cherry leaf extract 75%). The conclusion of this research was cherry leaf extract had antibacterial power against Streptococcus viridans. The concentration of cherry leaf extract which had the greatest inhibitory effect on Streptococcus viridans was 75%. Abstrak Streptococcus viridans dapat menyebabkan endokarditis bakterial subakut pada manusia. Dokter gigi harus hati-hati dalam melakukan perawatan saluran akar. Irigasi merupakan salah satu tahapan dalam perawatan saluran akar. Bahan yang biasanya digunakan adalah sodium hipoklorit. Sodium hipoklorit dapat mengiritasi jaringan. Bahan alternatif diperlukan seperti daun kersen (Muntingia calabura L.) dimana memiliki kandungan aktif flavonoid, saponin, dan tanin yang berperan sebagai antibakteri. Untuk mengetahui daya antibakteri ekstrak daun kersen terhadap Streptococcus viridans dan besar konsentrasi ekstrak daun kersen yang memiliki daya hambat terbesar terhadap Streptococcus viridans. Penelitian ini terdiri dari 5 kelompok, yaitu K+ (sodium hipoklorit), P1 (ekstrak daun kersen 12,5%), P2 (ekstrak daun kersen 25%), P3 (ekstrak daun kersen 50%), P4 (ekstrak daun kersen 75%). Media BHI-A ditanami suspensi Streptococcus viridans. Selanjutnya kertas cakram yang sudah diberi larutan sesuai kelompoknya diletakkan di atas media BHI-A tersebut. Meida diinkubasi selama 24 jam, lalu diameter zona hambat diukur. Zona hambat terbesar yaitu pada kelompok P4 (ekstrak daun kersen 75%). Kesimpulan dari penelitian ini ekstrak daun kersen memiliki daya antibakteri terhadap Streptococcus viridans. Konsentrasi ekstrak daun kersen yang memiliki daya hambat terbesar terhadap Streptococcus viridans adalah sebesar 75%. irigasi saluran akar perawatan saluran akar streptococcus viridans