Objectives: This study is aimed at evaluation of bacterial air contamination in intensive poultry breeding. The evaluation was based on the determined levels of bacterial concentrations and qualitative identification of isolated microorganisms. Materials and Methods: The study covered 5 poultry houses: two hatcheries and three hen houses with the litter bed system. The air was sampled in three measurement series in the central part of the investigated workplace at the height of about 1.5 m over the ground, using portable measuring sets consisting of a GilAir 5 (Sensidyne, USA) pump and a measuring head filled with a glass microfibre filter (Whatman, UK). For the quantitative and qualitative analysis of microorganisms were used appropriate microbiological media. Results: The total concentrations of airborne mesophilic bacteria inside the poultry breeding houses ranged from 4.74×104 cfu/m3 to 1.89×108 cfu/m3. For Gram-negative bacteria, the range comprised the values from 4.33×102 cfu/m3 to 4.29×106 cfu/m3. The concentrations of the cocci of Enterococcus genus ranged from 1.53×104 cfu/m3 to 1.09×107 cfu/m3, whereas those of other Gram-positive bacteria from 3.78×104 cfu/m3 to 6.65×107 cfu/m3. The lowest concentrations of each group of the examined microorganisms were noted in the second measurement series when the air exchange in the breeding houses was over twice higher than in first and third measurement series because the mechanical ventilation was supported by natural ventilation (opened gates in the buildings). The lowest concentrations of total bacteria were obtained in those buildings where one-day old chickens were kept. Gram-positive bacteria of the genera: Staphylococcus, Enterococcus, Corynebacterium, Brevibacterium, Micrococcus, Cellulomonas, Bacillus, Aerococcus, and Gram-negative bacteria of the genera: Pseudomonas, Moraxella, Escherichia, Enterobacter, Klebsiella, Pasteurella, Pantoea were isolated. It was shown that for most of the investigated livestock premises the total bacteria concentrations exceeded the reference value of 1.0×105 cfu/m3. Furthermore, pathogenic microorganisms which are a potential threat to human health (Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae ssp. ozaenae, Enterococcus faecalis, Enterococcus faecium) were found among the identified bacteria. Conclusions: The results indicate that the hygienic conditions of the working environment connected with litter bed system production of poultry are affected by changes of the efficiency of ventilation and create a direct health risk to employees. They should use personal protective measures to protect their respiratory tract, especially when the gates in the hen houses are closed.