KK-42 is an imidazole insect growth regulator. A (KK-42)-binding protein (KK-42BP) has been shown to be associated with diapause termination in pharate first instars of Antheraea yamamai (Guérin-Méneville) (Lepidoptera: Saturniidae). In this study, the (KK-42)-binding protein gene (ApKK-42BP) was characterized from Antheraea pernyi (Guérin-Méneville) (Lepidoptera: Saturniidae) undergoing a winter diapause as a pupa. Homologous comparison revealed that KK-42BPs from A. pernyi and A. yamamai were closely related to the known minor yolk proteins from the lepidopterans Bombyx mori L., Plodia interpunctella (Hübner), and Galleria mellonella L. The two KK-42BPs also contained a lipase-like region, as observed in the known lepidopteran yolk proteins. Phylogenetic analysis suggested that KK-42BP is a new member of the minor yolk proteins. Reverse transcription-polymerase chain reaction analyses showed that ApKK-42BP mRNA was expressed in all of the tissues tested, throughout four developmental stages, and in both female and male. Both in the brain and hemolymph, expression of ApKK-42BP mRNA level was similar between nondiapause-destined and diapause-destined larval individuals. ApKK-42BP mRNA was expressed in the predia-pause period of diapause-destined pupae, disappeared in early diapause and diapause stage, and reappeared in the postdiapause stage. These expression patterns stated that a lack of KK-42BP is associated with pupal diapause and its expression may be critical to nondiapausing individuals. Our results suggested that the KK-42BP gene is likely involved in a function other than as a yolk protein.