Background: Biodentin is a pulp capping material that has perfected the shortcomings of Ca(OH)2, but has low radiopacity and lower washing out resistance, so it is hoped that there will be natural ingredients that can be used as pulp capping materials. The nano brown anchovy has antibacterial content in the form of fluoride. Its nano size can also facilitate penetration better. Purpose: Analyzing the antibacterial potency of nano brown anchovy on mixed bacteria in deep carious dentine. Methods: The research was conducted in an experimental laboratory in vitro with a post-test only control group design. Brown anchovy was converted into nanoparticles then diluted into several concentrations using the broth dilution method. Direct contact method was used between nano anchovy and various concentrations of bacteria. The values of MIC (Minimum Inhibitory Concentration) and MBC (Minimum Bacterial Concentration) were obtained by counting the number of bacterial colonies growing on Mueller Hinton Agar media. Colony growth was calculated manually in Colony Forming Units (CFU). Data were analysed by One Way Anova test followed by a Tukey HSD test. Results: The MIC value at a concentration of 0.781% and the MBC value at a concentration of 1.56%. In positive control, there was an average bacterial death of 0%, a concentration of 0.781% had an average bacterial death of 91%, and at a concentration of 1.56% the average bacterial death was 100%. The results showed that the greater the concentration of nano anchovy, the stronger the antibacterial power. Conclusion: There is antibacterial potency in nano brown anchovy against Mixed Bacteria in deep dentin caries lesions.