In this study, the effect of aerosolized and water-supplemented Lactobacillus casei, L. plantarum and Saccharomyces cerevisiae fermented herbal extract (FHE) on air quality and immune response of broilers was studied. The experiments were performed in commercial broiler barns each accommodating 22,000 broiler chicks. Chickens kept in the house that were fogged twice daily with 20 l FHE (10 % in tap water) and provided with FHE in drinking water were compared with those in a comparable non-treated house. The total dust, airborne bacteria and endotoxins were significantly reduced in the FHE-fogged house. Chickens treated with FHE had significantly higher total IgY, better immune response to Newcastle disease vaccination and greater body weight (2 %), while serum avidin was significantly reduced compared with non-treated chickens. On the other hand, water fogging significantly decreased the total dust in a treated house compared with untreated house. However, cold fogging of water did not significantly decrease the cultivable airborne microorganisms in the treated house, and there was no significant difference in hemagglutinating antibodies in chickens of the water-fogged and non-treated houses. Body weights and mortality rates between the water-fogged and non-treated houses were not significantly different as well. These results suggest that cold fogging and oral applications of FHE could reduce the bioaerosols in poultry farms and improve the immune system of chickens.