Introduction: The Morus nigra (Moraceae) known as black mulberry is a well-grown plant in Lembang, Indonesia. Previous studies showed that black mulberry fruit has activity as antibacterial and antioxidant. The aims of this study were to evaluate the antibacterial effect of ethanol extract from stem bark, fruit, and leaves of Morus nigra, MIC and morphological changes of the most active extract against Staphylococcus epidermidis and Propionibacterium acnes. Methods: Agar diffusion and microdilution assays were used to evaluate the antibacterial effect of the extract by measuring the zone of inhibition and the minimum inhibitory concentration (MIC) of the extract against the test bacteria. Scanning electron microscopy (SEM) was performed to evaluate the morphological changes induced by the extract in cellular membrane of the bacteria. Protein and ion leakage from the bacterial cells induced by the extract were also evaluated. Results: The antibacterial activity showed the most active extract was an ethanol extract of the stem bark against S. epidermidis and P. acnes with MIC value 4 mg/ml and 2 mg/ml, respectively. The extract also induced protein and ion leakage in test bacterial cells. SEM findings revealed that the extract induced potential cellular membrane damage in 4xMIC. Conclusion: The antibacterial activity was related to the damaged of bacterial cell wall.