In this study, pollen grains in the atmosphere of Bilecik were studied for a continuous period of 2 years (2005 and 2006) by using Durham sampler. During this period, pollen grains belonging to 46 taxa were recorded, 26 of which belonged to arboreal plants and 20 to non-arboreal. Of total 14,269 pollen grains determined in Bilecik atmosphere, 6,675 were recorded in 2005 and 7,594 were in 2006. From these, 75.74% were arboreal, 21.80% were non-arboreal and 2.47% unidentifiable. Pinus sp., Poaceae, Cupressaceae, Platanus sp., Quercus sp., Salix sp., Ailanthus sp., Fagus sp., Urticaceae, Chenopodiaceae/Amaranthaceae were the main pollen producers in the atmosphere of Bilecik, respectively. Pollen concentrations reached their highest levels in May. Atmospheric pollen concentrations in February, March, September, October and November were less than those in other months.