The study of inner ear specific transcripts has revealed novel information about hereditary hearing loss and a mechanism of normal hearing. In this study, by analyzing a published cDNA library, we focused on Epiphycan (Epyc), a member of the small leucine-rich repeat proteoglycan family, whose transcript is enriched in the inner ear. Epyc mRNA was expressed abundantly and specifically in adult mice cochleae and was localized in supporting cells within the organ of Corti of both neonatal and adult mice. To examine the function of Epyc, we generated Epyc knockout (KO) mice using the CRISPR/Cas9 system. Epyc KO mice cochleae exhibited normal morphology. However, measurement of the auditory brain-stem response in Epyc KO mice revealed an elevated hearing threshold above 16 kHz frequency. This study suggests that Epyc is necessary for normal auditory function. (C) 2017 Elsevier Inc. All rights reserved.