Little is known about molecular mechanisms that control theDrosophilacircadian clock beyond the transcriptional–translational feedback regulation of clock genes as an intracellular process. In this study,Early gene at 23(E23) was identified as a novel clock gene that encodes the membrane-bound ABC transporter that is induced by the molting hormone ecdysone.E23expresses in pacemaker neurons in fly head, and its knockdown flies lengthened circadian period with an increased expression of the clock genevrille. E23andvrilleresponded to both ecdysone and clock signals, whereas E23 protein specifically suppressed the ecdysone response and is necessary for rhythmicity. Thus,E23forms its own feedback loop in the ecdysone response to control circadian oscillation through ecdysone-mediatedvrilleexpression. The ecdysone signaling pathway withE23is essential not only in developmental stage but also for the circadian behavior in adult fly.