The neurotrophin receptor p75 (p75NTR) is expressed in the developmental stage of the cochlea. However, the role of the p75NTR in the inner ear remains to be established. In this study, we conducted electrophysiological and morphological analyses of the auditory function of mice carrying a mutation in the p75 gene at different longitudinal stages. The mice carrying a mutation in the p75 gene showed an age-related progressive hearing loss. At 1 month, there was no obvious morphological change in the cochlea of the mice carrying a mutation in the p75 gene compared to wild-type mice, except for a slight loss of spiral ganglion neurons (SGNs). Auditory function was not significantly different between both genotypes from 1 to up to 4 months of age. The mice carrying a mutation in the p75 gene started to show progressive hearing loss at 4 months, when both SGN degeneration and hair cell (HC) loss were observed at the basal turn. These results suggest that the neurotrophin receptor p75 may play a significant role in the maintenance of cochlear function, and that mice carrying a mutation in the p75 gene could be a good animal model of early onset progressive hearing loss.