eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2017-12-21 10 4 1701 1708 10.13005/bpj/1282 17386 article Samah Ahmed Kadhum 1 University of Babylon, College of Pharmacy, Head of Department of Clinical Laboratory Sciences. In this study, we measured the antimicrobial activity of two types of nano-particles ZnO & SiO₂ against different types of (G⁺ & G^-) bacteria. We collected 90 samples from four sites of infections (burn, wound, urine & sputum) to isolate the following bacteria from hospitalized patients: P. aeruginosa, K. pneumoniae & E. coli as gram-negative bacteria (about 15 swabs for each one) and the other were S. aureus, S. epidermidis & S. pneumoniae as gram-positive bacteria (about 15 swabs for each one). After collecting the samples we diagnosed these bacteria by culturing and biochemical tests and we prepared ZnO & SiO₂ nano-particles by chemical method through surface modification in the structure and morphological properties. The antibacterial activity of these nano-particles against different types of bacteria were measured by agar diffusion method, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). It was concluded that the best inhibition zone was (33 mm) at a concentration of 10 µg/ml of nano-ZnO in P. aeruginosa growth while the lower inhibition zone was (8 mm) at the concentration of 2 µg/ml at the same nano particle in S. epidermidis . It was also concluded that the best inhibition zone was (20 mm) at a concentration of  10 µg/ml of nano-SiO₂ in P. aeruginosa  while the lower inhibition zone was (2 mm) at the concentration of 4 µg/ml at the same nano-particle in  S. epidermidis with no inhibition zone at the concentration of 2 µg/ml observed in the same bacteria. We had noted that all tested bacteria were completely inhibited at the concentration of 1.25 µg/ml of nano-ZnO (MIC) with no significant antibacterial activity less than this concentration. The (MBC) was the same as (MIC) as compared with data which showed that all tested bacteria were completely inhibited at the concentration of 0.625 µg/ml of nano-SiO₂ and the (MBC) was the same as (MIC) for all tested isolates. So the two nano-particles (ZnO & SiO₂) had antibacterial activity, but nano- ZnO was better than nano-SiO₂ and could inhibit most of the important pathogenic bacteria at the tested concentrations isolated from hospitalized patients. https://biomedpharmajournal.org/vol10no4/the-effect-of-two-types-of-nano-particles-zno-and-sio2-on-different-types-of-bacterial-growth/ Antimicrobial  Aeruginosa bacteria Diagnosed