OBJECTIVE To develop gene expression profiles of young and old senescence-accelerated mouse (SAM) cochlea and identify genes responsible for aging-related hearing loss. METHODS Gene micro-array slides containing 1101 mouse genes were hybridized to cDNA micro-arrays (Atlas Glass Array Mouse 1.0) that were synthesized using total RNAs from the cochlea of 2 mounts and 12 mounts mouse. Hybridization signals were visualized with cyanine-3 fluorescent reporter molecules, and the fluorescence intensities of the images were analyzed. Real-time quantitative reverse transcription PCR (qRT-PCR) was performed to validate the micro-array results. Immunofluorescence was used to identify the located region of the protein encoding by the candidate gene in the cochlea. RESULTS Expression of a majority of the 1101 genes represented on the micro-array slides was not altered during aging; nonetheless, changes in the expression of 3 genes were detected between young and old mouse cochlea. RT-PCR results confirmed the changes in expression of thymosin beta4 of 3 genes examined. Through the using of immunofluorescence, it was shown that thymosin beta4 was primarily located in the tectorial membrane and the supporting cells of outer hair cell. CONCLUSIONS Using commercially available slide micro-arrays, the results show that aging of the mouse cochlea is associated with changes in patterns of gene expression. This analysis suggests that thymosin beta4 may play a role in aging-related hearing loss. These studies lay the foundation for future studies defining the genetic basis of aging-related hearing loss.