Methionine sulfoxide reductases (MsrA and MsrB) protect the biological activity of proteins from oxidative modifications to methionine residues and are important for protecting against the pathological effects of neurodegenerative diseases. In the current study, we characterized the auditory phenotype of the MsrA knockout mouse. Young MsrA knockout mice showed small high-frequency threshold elevations for auditory brainstem response and distortion product otoacoustic emission compared to those of wild-type mice, which progressively worsened in older MsrA knockout mice. MsrA knockout mice showed an increased sensitivity to noise at young and older ages, suggesting that MsrA is part of a mechanism that protects the cochlea from acoustic damage. MsrA mRNA in the cochlea was increased following acoustic stimulation. Finally, expression of mRNA MsrB1 was compromised at 6 months old, but not in younger MsrA knockout mice (compared to controls). The identification of MsrA in the cochlea as a protective mediator from both early onset hearing loss and acoustic trauma expands our understanding of the pathways that may induce protection from acoustic trauma and foster further studies on how to prevent the damaging effect of noise exposure through Msr-based therapy.