This study was carried out to measure temperature, humidity, and bacterial concentration and species from the indoor air of a greenhouse used for shiitake cultivation. The highest level of humidity in the greenhouse was recorded at over 91.5% and the lowest humidity was recorded at 50% during 12 months. Temperature was between 5.1-30.5oC except for January. These results indicate that bacteria can survive in the indoor air of the greenhouse. Total bacterial concentration exceeded the Korean indoor air quality standard value (8.0 × 102 cfu/m3) in winter. A total of 13 genera and 17 species were isolated and identified from the indoor air of the greenhouse. Especially, 3 species (Kocuria rosea, Staphylococcus xylosus and Curtobacterium flaccumfaciens) have been reported to affect on human health. This is first report of airborne bacteria in a greenhouse used for shiitake cultivation. Keywords : Bacterial concentration, Greenhouse, Indoor air quality, Shiitake, Species