To gather information on the indoor air quality of the greenhouses used for edible oakwood mushroom cultivation, temperature, humidity, and bacterial concentration and species were investigated in 2015 and 2016 in 21 mushroom greenhouses located in ten different regions in Korea. Temperature and humidity of all the mushroom greenhouses ranged from 16.2 to 30.8oC and from 28.2 to 85.6%, respectively. Bacterial concentration exceeded the Korean indoor air quality standard value (800 cfu/m3) in 15 of the 21 mushroom greenhouses. A total of 33 genera and 76 species were identified in the indoor air of the mushroom greenhouses investigated. Of the identified bacteria, 10 genera and 15 species including Acidovorax oryzae, Bacillus infantis, B. licheniformis, Cellulosimicrobium funkei, Ewingella Americana, Exiguobacterium sibiricum, Leclercia adecarboxylata, Lysinibacillus sphaericus, Pseudomonas fulva, Raoultella terrigena, Staphylococcus cohnii, S. haemolyticus, S. saprophyticus, S. sciuri, and Streptomyces sindenensis are among those known to have a harmful effect on human health. These bacteria have been reported to cause sepsis, skin infection, bloodstream infection, bacteremia, spondylitis, peritonitis, acute meningitis, endocarditis and urinary tract infection. The results of this study indicate that continuous hygiene management of indoor air is necessary in the greenhouses used for oakwood mushroom cultivation. Keywords: Bacterial concentration, Bacterial species, Greenhouse, Indoor air quality, Oakwood mushroom