Odorant-binding proteins (OBPs) primarily function in the transport of hydrophobic odorants. In this study, OBPs originating from rat and pig were cloned into a mammalian expression vector, pcDNA3, and expressed in HEK-293 cells, and their specificity for odorants and olfactory receptors was examined. Results suggest that OBPs have a high affinity for the olfactory receptors when both the OBP and receptor originate from the same species. The rat OBPs were bound not only to the rat olfactory receptor I7 but also to the odorant specific to I7. The solubility of the odorant was increased by both OBP2 and OBP3, which originate from rat, but with different efficiencies. These results demonstrate that OBPs specifically interact with odorants as well as olfactory receptors, and these interactions can influence the sensitivity of olfactory receptor-based biosensors.