Mammalian cochleae have limited capacity for regeneration, which is one of the major difficulties in the treatment of sensorineural hearing loss. In the current study, we examined the potential of bone marrow-derived stromal cells (BMSCs) for functional restoration of mouse cochleae through regeneration or maintenance of cochlear fibrocytes in the spiral ligament (SL). We used a mouse model of degeneration of cochlear fibrocytes in the SL using local application of 3-nitropropionic acid (3-NP), in which disruption of the gap junction network in the SL resulted in the reduction of the endocochlear potential (EP). Mouse BMSCs were infused into the posterior semicircular canal 7 days after 3-NP application. Transplanted BMSCs were frequently observed in the cochlear fluid space 4 weeks after transplantation, although a few transplants had migrated into the cochlear tissues including the SL. BMSC-treated cochleae exhibited higher cell densities in the SL and greater EP levels than the control ones. Immunohistochemistry further demonstrated the restoration of functional proteins in the SL. Significant recovery in thresholds of auditory brainstem responses following BMSC transplantation was found only at 40 kHz in a mild degeneration model. Our cumulative findings indicated that BMSCs accelerated regeneration or maintenance of fibrocytes in damaged SLs, leading to partial functional restoration of the mouse cochleae. Anat Rec, 303:478-486, 2020. © 2019 American Association for Anatomy.