Osmia species (Hym.: Megachilidae) are important because they can continue even their pollinator activity in orchards in the unfavourable weather conditions for honey bees. In the study, the pollen encountered in the artificial nests of Osmia bicornis (L.) and O. caerulescens (L.) used for supporting their populations in the sweet cherry orchards were analysed. The nests were established in two cherry orchards of Sultandağı town (Afyonkarahisar, Turkey) in April of 2009 and 2010 and removed in September of the same years. Pollen samples were obtained from total 11 nests of O. bicornis and 6 nests of O. caerulescens. Total 4800 pollen grains were examined. As a result of the diagnosis studies of pollen grains, it determined that two species collected the pollens of 6 families and that the dominant pollen group belonged to the Brassicaceae (60.1%) for O. bicornis while Fabaceae (48.2%) for O. caerulescens. The second pollen group were Rosaceae (20.7%) for O. bicornis while Asteraceae (11.8%) for O. caerulescens. In the nests of O. caerulescens, 2.8% Rosaceae pollen were encountered. According to these results, the effect of O. bicornis is higher than O. caerulescens’s on sweet cherry pollination.