The water fraction of durian peel (Durio zibethinus Murray) contains compounds chemical flavonoids, saponins, tannins and alkaloids which have antibacterial effects against Streptococcus mutans bacteria. The aim of the study was to determine the water fraction of durian (Durio zibethinus Murray) can be formulated into a mouthwash and has activity as an antibacterial in inhibiting the growth of Sterptococcus mutans bacteria. Experimental research method with maceration extraction using 96% ethanol solvent, then a mouthwash formulation was made with concentrations of FI (1%), FII (5%), and FIII (10%), and tasted for antibacterial activity with the Paperdisk method. The results showed that water fraction durian skin mouthwash (Durio zhibetinus Murray) on organoleptic testing, pH, and stable viscosity before and after cycling test. Mouthwash water fraction of durian skin (Durio zibethinus Murray) has antibacterial activity FI 8.5 mm, FII 11.9 mm and FIII 15.4 mm against Streptococcus mutans. The mouthwash of the water fraction of durian skin (Durio zhibetinus Murray) is stable physically and chemically and has the best antibacterial activity inhibiting growth of Streptococcus mutans bacteria in FII (5%) and FIII (10%) with strong inhibition zone category. Keywords: Water fraction of durian peel, mouthwash, antibacterial, Streptococcus mutans Abstrak Fraksi air kulit durian (Durio zibethinus Murray) memiliki kandungan senyawa kimia flavonoid, saponin, tanin dan alkaloid yang memiliki efek antibakteri terhadap bakteri Streptococcus mutans. Tujuan penelitian untuk mengetahui fraksi air kulit durian (Durio zibethinus Murray) dapat diformulasi menjadi sediaan obat kumur serta memiliki aktivitas antibakteri terbaik dalam menghambat pertumbuhan bakteri Streptococcus mutans. Metode penelitian secara eksperimental dengan ekstraksi secara maserasi menggunakan pelarut etanol 96%, lalu dibuat formulasi sediaan obat kumur dengan konsentrasi FI (1%), FII (5%), dan FIII (10%), dan uji aktivitas antibakteri dengan metode Papperdisk. Hasil penelitian menunjukkan bahwa obat kumur fraksi air kulit durian (Durio zhibetinus Murray) pada pengujian organoleptik, pH, dan viskositas stabil sebelum dan setelah Cycling test. Obat kumur fraksi air kulit durian (Durio zibethinus Murray) memiliki aktivitas antibakteri FI 8,5 mm, FII 11,9 mm, dan FIII 15,4 mm terhadap bakteri Streptococcus mutans. Obat kumur fraksi air kulit durian (Durio zhibetinus Murray) stabil secara fisika dan kimia serta memiliki aktivitas antibakteri terbaik menghambat pertumbuhan bakteri Streptococcus mutans yaitu pada FII (5%) dan FIII (10%) dengan kategori zona hambat kuat. Kata Kunci: Fraksi air kulit durian, obat kumur, antibakteri, Streptococcus mutans