Introduction: In the current  research, the effectiveness of silver's Nano- particles anti- microbial activity on the pathogenic and resistant positive- gram and negative-gram bacteria in the hospital infections have been studied. In this study, the primary density of bacteria was constant and only Nano- particles and items of studied bacteria were variable.

Materials & methods: At first, this study uses the available chemical reagents and conditions only apply controlling optimum conditions, nanoparticles with a size of about 20-35 nm were synthesized by chemical precipitation method. Using Macro dilution  method the different densities of silver Nano- particles and Zinc Nano- particles (medium+ Nano- particle) were prepared as: 0.01 percent, 0.1 percent, 0.5 percent, 1 percent and 1.5 percent. Then density of 1.5 cell/ml was prepared for Staphylococcus aureus Pseudomonas aeruginosa the containers which included treatment medium (bacterium + Nano- particle) and control medium have been placed in incubator shaker with 250 cycle in minute and 37˚C for 24h. after passing this time, light density 600 nm ware length was used for measuring bacteria density, then OD in treatment and + control and – control were determined. Nano- particles dilutions were used in bacteria medium for calibrating spectrophotometer as a blank solution. . These results are statistically significant. (P-value <0.01).

Findings: Statistical analysis about Zn Ag Nano- particles showed that in 0.5 percent density Nano- particles were bactericide and they could eliminate 100% of Staphylococcus aureusPseudomonasaeruginosa and in 0.01 percent density for all two bacteria, these Nano- particles were bacteriostatic.

Discussion & Conclusion: in the laboratorial tests of Nano-Materials, contact with them, bacteria will be killed. The obtained results for Nano- particles' anti- bacteria property showed that there is a direct relationship between Nano- particles density and the amount of bacteriums elimination.