- The objective of this study was to assess the level of air contamination by bacteria in the broiler houses in salamieh region that Famed of commercial breedings of broiler and relationship with some impact factors like (birds age- season-breeding system - dust concentration) . - The numbers of bacteria (mesophile , staphylococci , streptococci and gram-negatives) and dust concentration were determined in 5 opened broiler houses and 5 closed broiler houses with chicken houses in different ages (1-6 weeks old) in summer and winter .