Background: Acinetobacter baumannii is a Gram-negative, obligate anaerobic, non-fermented and non-motile bacterium. Acinetobacter baumannii has become a particularly important organism in the Intensive Care Unit (ICU). Acinetobacter baumannii plays a significant role in nosocomial infections. Multidrug- resistant A. baumannii is recognized to be among the most difficult antimicrobial-resistant Gram-negative bacilli to be controlled and treated. For this reason, we examined the efficacy of nanosilver material against different types of bacteria.Methods: Silver nanoparticles with sizes of 20 nm were obtained from the Pishtazan nanotechnology (Mashhad-Iran). Then, silver nanoparticles serial dilutions (40000, 20000, 10000, 5000, 2500, 1250, 625, 312 ppm) were prepared in nutrient broth medium and 1.5 x 106 bacteria were added to each tube. After 24 h incubation at 37oC, the MIC (minimum inhibitory concentration) and MBC (minimum bactericide concentration) were determinate by sub-culturing and colony counting on Mueller Hinton agar. Also, we evaluated the antibacterial properties of nano silver by disk diffusion and well diffusion methods (30 ml 10,000 ppm solution per well and per disk) in this research. This study antibacterial activity of silver nanoparticles was tested for 20 clinical Acinetobacter baumannii (collected from Imam Reza Hospital in Tabriz) as a standard strain.Results: The MIC and MBC of silver nanoparticles (20 nm) were 1200 ppm and 2500 ppm for all clinical isolated Acinetobacter baumannii. The zone of dick diffusion and well diffusion methods respectively were 9 mm and 7 mm. The MIC and MBC results obtained for clinical isolates Acinetobacter baumannii showed no significant difference.Conclusion: Acinetobacter baumannii is susceptible to silver nanoparticles. Also the same MIC and MBC in multiple clinical strains suggest that there is no resistance to silver nanoparticles in Acinetobacter baumannii.