Hearing impairment is the most frequent disability in elderly individuals; however, we have limited options for treatment of age-associated hearing loss. To establish novel strategies for the treatment of age-associated hearing loss, it is crucial to elucidate the mechanisms of age-associated hearing loss. Studies on animal models and human temporal bones have indicated a close relationship between degeneration of the spiral ganglion neurons and stria vascularis and age-associated hearing loss. We have developed a drug delivery system using biodegradable gel for the inner ear to protect inner ears against aging. In addition, recent studies on cell therapy for the inner ear have suggested the efficacy of cell transplantation for restoration of hearing.