Background and Objectives: Nanotechnology is the production, use and development of tools and materials whose dimensions are about 1 to 100 nm. Silver nanoparticles are used in packaging, cosmetics, health, medical and poultry industries. Due to the excessive application of silver nanoparticles with its broad antibacterial properties, the evaluation of biocompatibility of silver nanoparticles on biological systems appears to be necessary. The aim of this study is to investigate the effects of nanosilver on blood cells in rats.Materials and Methods: In this study, silver nanoparticles with doses of 25, 50, 100 and 200 mg/kg body weight orally administered for 28 days to 50 male rats were placed in five groups each of which with ten rats. Then, blood samples were taken from rats; finally, blood cell count was determined and blood coagulation tests were performed.Results: In this study, no significant changes on the number of blood cells including white blood cells, red blood cells, and platelets were observed in any of the doses used. Despite normal blood clotting time at all doses tested, bleeding time test and clot retraction test showed significant changes at high doses, i.e. 200 mg/kg body weight of rats.Conclusions: The increased bleeding time and decreased percentage of the serum collected are the consequence of the suppressive effect of silver nanoparticles on the clotting function of platelets in high doses.