The antimicrobial properties of essential oils have been demonstrated by various in vitro studies, whereas their effect on poultry farm hygiene has not been thoroughly investigated, in particular with reference to aerial treatment. The present study aims to assess the antibacterial effects of natural essential oils in broiler houses. Two experimental rooms were fogged with aqueous solutions of peppermint and thyme oils. The control room was sprayed with pure water. The experiment was conducted on broilers aged 1 to 42 d. The rooms were fogged every 3 d. One day after fogging, the total counts of mesophilic aerobic bacteria, Enterobacteriaceae, and mannitol-positive staphylococci were determined. Samples were collected from the air, litter, walls, and drinkers. The results of the study demonstrate that essential oil mist may improve hygiene standards in broiler farms. During broiler growth, the mean total counts of mesophilic bacteria in the rooms treated with essential oils were lower (P < 0.01 or P < 0.05) in comparison with the control. Enterobacteriaceae and staphylococci counts were also higher in the control group. A single exception was noted in a litter sample where the mean count of Enterobacteriaceae in the room fogged with peppermint oil was higher than in the control. Both oils reduced bacterial counts, but thyme oil was more effective in reducing coliform bacteria, whereas peppermint oil had a higher inhibitory effect on the proliferation of staphylococci. These promising results encourage further research to determine the optimal doses and the effects of essential oils and their combinations on the living conditions and health status of broiler chickens.