The purpose of this study was to investigate the antimicrobial activity of silver nanoparticles (AgNPs) biosynthesized by isolated Escherichia hermannii obtained from aquacultured fish on several human pathogens. AgNPS were isolated once E. hermanii had been isolated from the organs of Cyprinus carpio L. and Tinca tinca. The biosynthesis of AgNPs was measured using a UV-visible and FTIR analysis. The antimicrobial activity of AgNPs was evaluated using the well diffusion method. MIC values were determined and compared with the results obtained using commercial antibiotics for positive control. The antimicrobial activities of AgNPs at two different concentrations (0.5mM, 1mM) were measured using the diameter of inhibition zone (DIZ). Although AgNPs exhibited several degrees of antimicrobial effect on the microorganisms (DIZ values between 8 and 25 mm) included in the study, the highest effects were observed against Listeria monocytogenes, Salmonella typhimurium, Candida albicans (DIZ=25mm), and Shigella dysenteria (DIZ=20mm) at a concentration of 1 mM AgNPs. No antimicrobial effect was observed against Proteus mirabilis. The results obtained are thought to be an effective antibacterial agent against human pathogens by the biosynthesis AgNPs of E. hermannii and based on the data of the obtained indices, these AgNPs can be considered as an alternative to today's antibiotics.