Antibacterial Activity of The Gamal Leaf (Gliricidia sepium) Ethanol Extract on the Growth of Streptococcus mutans. Streptococcus mutans is a positive gram bacteria which cause dental caries. From the several previous studies, Gamal leaf has been predicted as the antibacterial agent because of their active substance such as tannins, alkaloids, saponins, and flavonoids. The objective of the study was to know the antibacterial activity of ethanol extract of Gamal leaf (Gliricidia sepium) for Streptococcus mutans in various concentrations. This study was a true experimental with post-test only control design. The determination of antibacterial activity in this study was conducted by using Kirby Bauer disk diffusion method with the various concentrations, there were 40, 50, 60, 70 and 80%. The positive and negative controls in this study were 30 µg disk diffusion of chloramphenicol and the 96% of ethanol. The average inhibition of zone diameter in the concentrations of 40, 50, 60, 70 and 80% were 11.3, 12.3, 13.4, 15.3 and 19.2 mm, respectively. One Way ANOVA statistical analysis showed that the value of p was 0.000, it can be concluded that the ethanol extract of Gamal leaf (Gliricidia sepium) have strong antibacterial activity, especially to Streptococcus mutans bacteria. Abstrak: Aktivitas Antibakteri Ekstrak Etanol Daun Gamal (Gliricidia sepium) pada Berbagai Konsentrasi terhadap Pertumbuhan Bakteri Streptococcus mutans secara In-Vitro.Streptococcus mutans merupakan bakteri gram positif penyebab utama terjadinya karies gigi. Berdasarkan beberapa hasil riset terdahulu, daun gamal diperkirakan memiliki aktivitas antibakteri yang cukup baik karena kandungan beberapa senyawa metabolit sekundernya seperti tanin, alkaloid, saponin, dan flavonoid. Penelitian ini bertujuan mengetahui aktivitas antibakteri ekstrak Etanol daun gamal (Gliricidia sepium) pada berbagai konsentrasi terhadap pertumbuhan bakteri Streptococcus mutans secara in-vitro. Metode penelitian true experimental dengan desain penelitian post-test only control design. Penentuan aktivitas anti bakteri dilakukan dengan menggunakan metode difusi cakram Kirby Bauer dengan lima konsentrasi uji yaitu konsentrasi 40, 50, 60, 70 dan 80%. Kontrol positif berupa cakram disk antibiotik Kloramfenikol 30µg dan kontrol negatif yaitu Etanol 96%. Berdasarkan hasil penelitian, diketahui bahwa rata-rata diameter zona hambat pada konsentrasi 40, 50, 60, 70 dan 80% berturut-turut adalah sebesar 11,3; 12,3; 13,4; 15,3 dan 19,2 mm. Uji statistik One Way Anova dengan nilai p 0,000 disimpulkan bahwa ekstrak etanol daun gamal (Gliricidia sepium) memiliki aktivitas antibakteri yang kuat, terutama terhadap bakteri Streptococcus mutans.