Striatin, a subunit of the serine/threonine phosphatase PP2A, is a core member of the conserved striatin-interacting phosphatase and kinase (STRIPAK) complexes. The protein is expressed in the cell junctions between epithelial cells, which play a role in maintaining cell-cell junctional integrity. Since adhesion is crucial for the function of the mammalian inner ear, we examined the localization and function of striatin in the mouse cochlea. Our results show that in neonatal mice, striatin is specifically expressed in the cell-cell junctions of the inner hair cells, the receptor cells in the mammalian cochlea.Auditory brainstem response measurements of striatin-deficient mice indicated a progressive, high-frequency hearing loss, suggesting that striatin is essential for normal hearing. Moreover, scanning electron micrographs of the organ of Corti revealed a moderate degeneration of the outer hair cells in the middle and basal regions, concordant with the high-frequency hearing loss. Importantly, striatin-deficient mice show aberrant ribbon synapse maturation that may lead to the observed auditory impairment. Together, these results suggest a novel function for striatin in the mammalian auditory system. Medicine Grant for Collaborative Research (RL, RRA). We thank Ana Turchetti-Maia and Kevin Ohlemiller for their advice for EP recordings, Vered Holdengreber for help with electron microscopy, and Ronen Siman-Tov for help with the mice. Author contributions KBA and RRA conceived the project. RAL generated the Striatin knockout mice. PTNP designed and performed the genotyping, dissections of inner ears, ABR, SEM, confocal imaging, Western blots, and quantification of ribbon synapses. MR and ST performed the endocochlear potential experiments. ST and TK-B aided with dissections and SEM imaging analysis. MC and AAD aided with image analysis, experimental design and organizing the data. PTNP, ST, KBA, and RRA wrote the manuscript. KBA and RRA supervised the work.