Background and Objective: Metronidazole has played an important role in anaerobic-related infections. It is used clinically to treat gingivitis, acute necrotizing ulcerative gingivitis, chronic periodontitis and aggressive periodontitis. The newly used nanoparticles loaded with the antibiotics have been introduced in the treatment of many infections. The aim of the present study was to compare between the antibacterial effect of silver nanoparticles, metronidazole and metronidazole carried on silver nanoparticles on Porphyromonas Gingivalis (P.gingivalis) in vitro.Materials and Methods:Minimal inhibitory concentration (MIC) for the silver nanoparticles, metronidazole and the combined use of nanoparticles and metronidazole were determined. Tube dilution methods were performed and weighted in an analytical balance.Results: metronidazole loaded on Silver Nanoparticles was the most efficacious with a MIC of 0.0625 μg/ml while MIC was 0.125 µg/ml for metronidazole and 1 μg/ml for silver nanoparticles. In group III (metronidazole loaded on Silver Nanoparticles) the reduction in number of P.gingivalis was significantly greater than two other groups. Conclusion: Silver nanoparticles could have a synergistic effect with metronidazole, controlled release of metronidazole increases its effect in metronidazole loaded on silver nanoparticles group and metronidazole has an effective antimicrobial activity compared to silver nanoparticles at low concentration.