Abstract: Butterflies contain chemosensory organs for selecting host plants, with a specialized chemoreception system for laying eggs on plants. The cabbage butterfly, Pieris rapae, oviposits selectively on cabbage (Brassicaceae), and the swallowtail butterfly, Atrophaneura alcinous on pipevine (Aristolochiaceae). The oviposition of butterflies is induced by the recognition of specific host plant components using tarsi on the forelegs. Although oviposition stimulants from the host plants have been characterized for several species of butterflies, the chemoreception mechanism(s) in butterflies for oviposition remains unclear. This chapter focuses on clarifying the chemotransduction mechanism of oviposition in the swallowtail butterfly, A. alcinous, based on previous work (Tsuchihara et al. 2001; 2009a; 2009b) and adds new findings for morphological and physiological specialization of female taste sensilla. A. alcinous requires a simple combination of the stimulants, hydrophilic sequoyitol and lipophilic aristolochic acid, for oviposition compared with other species of butterflies.