Infectious disease caused by bacteria have been a major suffered disease in developing countries for instance Indonesia. There have been pathogenic microorganisms reported being resistant to existing antibiotics, hence it is necessary to conduct research to find new antimicrobials derived from natural ingredients. Research entitled “Antibacterial Activity Testing of Pedada(Sonneratia caseolaris) Extract in Resisting Escherichia coli Bacteria” has research question of whether Pedada extract has antibacterial activity in resisting the growth of Escherichia coli bacteria. This research aimed to provide scientific information of Pedada extract antimicrobial activity against Escherichia coli bacteria since the information of this plant is still rarely found. Pedada was extracted using maceration method with 96% ethanol as solvent. Extract of Pedada was tested for antibacterial activity against Escherichia coli by diffusion method which the well cup method in varies concentration of 0.2 g, 0.4 g, 0.6g, and 0.8g. Cotrimoxazole was used as a positive control and DMSO was used as a negative control. The result obtained was resistor zone diameter. Based on the data obtained from the concentration of Pedada extract, namely 20%, 40%, 60%, 80%, indicating the diameter of the inhibition zone respectively 10.2 ± 0.34 mm, 11.8 ± 0.51 mm, 14.1 ± 0.51 mm, 17.6 ± 1.0 mm. Based on the data analysis, it was concluded that pedada extract (Sonneratia caseolaris) had antibacterial activity against Escherichia coli bacteria.