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Abstract Transforming growth factor-β (TGF-β) signaling plays a significant role in multiple biological processes, including inflammation, immunity, and cell death. However, its specific impact on the cochlea remains unclear. In this study, we aimed to investigate the effects of TGF-β signaling suppression on auditory function and cochlear pathology in mice with kanamycin-induced ototoxicity. Kanamycin and furosemide (KM-FS) were systemically administered to 8-week-old C57/BL6 mice, followed by immediate topical application of a TGF-β receptor inhibitor (TGF-βRI) onto the round window membrane. Results showed significant TGF-β receptor upregulation in spiral ganglion neurons (SGNs) after KM-FA ototoxicity, whereas expression levels in the TGF-βRI treated group remained unchanged. Interestingly, despite no significant change in cochlear TGF-β expression after KM-FS ototoxicity, TGF-βRI treatment resulted in a significant decrease in TGF-β signaling. Regarding auditory function, TGF-βRI treatment offered no therapeutic effects on hearing thresholds and hair cell survival following KM-FS ototoxicity. However, SGN loss and macrophage infiltration were significantly increased with TGF-βRI treatment. These results imply that inhibition of TGF-β signaling after KM-FS ototoxicity promotes cochlear inflammation and SGN degeneration.