In order to identify the major bacterial agents, causing nosocomial infections and also detection of resistancy drugs to current antibiotics, a cross -sectional study was carried out in three hospitals of Medical Sciences University of Hamadan. In this study 712 samples were collected from different parts of emergency section, injection and dressing rooms, and patients rooms. The samples were cultured on E. M. B and Blood agar by sterile wet cotten swab. A smear was also prepared for gram staining dye. After detection of bacterial agents, 174 strains were performed for antibiogram by agar disk diffusion method. The mean of frequency of contamination was 48.6% in three hospitals. The distribution of gram negative bacteria was 52.3% and gram positive bacteria was also 47.7%. The highest contamination was obtained from emergency sections but the lowest contamination was in injection and dressing rooms. The most important bacteria were: Staph aureus and epidermidis, E. coli, Bacillus subtilis, Klebsiella, Enterobacter, Pseudomonas, Lactobacilli, Diphtheroieds and Entercocci.The most drugs resistancy was observed in staphilococci, E. coli, Klebsiella, Enterococci and Pseudomonas aueroginosa. There was high resistancy for Ampicillin, Tetracycline, sulfametaxazlo, Penicillin and cephalexin.