Tujuan penelitian ini untuk mengetahui senyawa metabolit sekunder yang terkandung dalam ekstrak etanol kulit batang tanaman mengkudu (Morinda citrifolia L.) berdasarkan uji skrinning fitokimianya dan menentukan aktivitas bakteri terhadap bakteri Escherichia coli dan Staphylococcus aureus. Penelitian diawali tahap ekstraksi yaitu metode maserasi dilanjutkan uji skrinning fitokimia. Uji aktivitas antibakteri digunakan metode difusi cakram. Diperoleh ekstrak kental etanol berwarna hijau kehitaman sebanyak 468,3 gram. Hasil uji skrinning fitokimia menunjukkan hasil mengandung senyawa steroid, flavonoid, alkaloid, fenolik, tanin. Hasil uji ekstrak etanol kulit batang mengkudu terhadap bakteri Staphylococcus aureus menghasilkan aktivitas antibakteri tergolong sedang pada konsentrasi 50% dan 60% serta aktivitas antibakteri tergolong kuat pada konsentrasi  70%,  dan 80% dengan zona hambat berturut-turut 16,75 mm; 19,75 mm; 21,5 mm; dan 21,75 mm. Sementara itu, menghasilkan aktivitas antibakteri yang tergolong sedang pada konsentrasi 50% serta aktivitas antibakteri yang tergolong kuat pada konsentrasi 60%, 70%, dan 80% dengan zona hambat berturut-turut  20 mm; 23 mm; 24 mm; dan 27,75 mm pada bakteri Escherichia coli. Kemampuan antibakteri antibiotik amoksisilin 10% sebanding dengan 70% ekstrak etanol kulit batang mengkudu pada bakteri Staphylococcus aureus dan sebanding dengan 60% ekstrak etanol kulit batang mengkudu pada bakteri Escherichia coli.

• The purpose of this research is to determine secondary metabolite compounds contained in ethanol extract of Morinda citrifolia L. stem bark based on phytochemical screening test and determine bacterial activity against Escherichia coli and Staphylococcus aureus bacteria. The study begins with the extraction stage, which is the maceration method followed by phytochemical screening. The antibacterial activity test using the disc diffusion method. Thick green ethanol extract obtained as much as 468.3 grams. Phytochemical screening test results show the results contain steroids, flavonoids, alkaloids, phenolic compounds, tannins. The results of ethanol extract of Noni stem bark against Staphylococcus aureus bacteria produced moderate antibacterial activity at concentrations of 50% and 60% and antibacterial activity classified as strong at 70% concentration, and 80% with inhibitory zones respectively 16.75 mm; 19.75 mm; 21.5 mm; and 21.75 mm. Meanwhile, the antibacterial activity was classified as moderate at a concentration of 50% and the antibacterial activity was classified as strong at a concentration of 60%, 70%, and 80% with a inhibitory zone of 20 mm respectively; 23 mm; 24 mm; and 27.75 mm in Escherichia coli bacteria. The antibacterial ability of amoxicillin 10% is equal to 70% of the noni stem bark ethanol extract in Staphylococcus aureus bacteria and is equivalent to 60% of the noni stem bark ethanol extract in Escherichia coli bacteria.