Our work describes the application of mass spectrometry-based label-free quantitative proteomics for the identification of differentially expressed proteins between different-aged cochlea. We report proteins exclusively present as well as up- and downregulated in the cochlear sensory epithelium at significant developmental stages. Additionally, we report proteins exclusively present on P3 that were recently identified in the cochlea for the first time. We use bioinformatics to provide insight on biological functions and potential primary and secondary partners of the differentially expressed proteins. This study provides the first differentially expressed proteome in the mammalian cochlea at significant developmental stages; before hearing, during the onset of hearing, and when hearing is fully developed. We believe that these results will provide insights into the function of proteins that change during development and identify potential protein biomarkers related to hearing impairments.