Objective To determine the effects of combined administration of furosemide and kanamycin on inner ear structures and the auditory nerve in rats. Methods The rats in the treatment group received intravenous injections of combined furosemide and kanamycin sulfate, and the rats in the normal control group received no treatment. The auditory brainstem response (ABR) test was carried out 7 days after drug administration to determine the effects of drug administration on hearing. Cochlear slice and cochlear wholemount were prepared after 7 days of drug treatment. Results After 7 days of drug administration, ABR thresholds were significantly higher in the treatment group than in the control group and neurofilaments were significantly reduced, although the number of spiral ganglia showed no decrease and there were no signs of supporting cell injury. Conclusions Combined administration of furosemide and kanamycin sulfate has an apparent synergistic ototoxic effect. Although spiral ganglion damage may not be apparent within a short time period of drug administration, damage to auditory nerve fibers is obvious. Objective To determine the effects of combined administration of furosemide and kanamycin on inner ear structures and the auditory nerve in rats. Methods The rats in the treatment group received intravenous injections of combined furosemide and kanamycin sulfate, and the rats in the normal control group received no treatment. The auditory brainstem response (ABR) test was carried out 7 days after drug administration to determine the effects of drug administration on hearing. Cochlear slice and cochlear wholemount were prepared after 7 days of drug treatment. Results After 7 days of drug administration, ABR thresholds were significantly higher in the treatment group than in the control group and neurofilaments were significantly reduced, although the number of spiral ganglia showed no decrease and there were no signs of supporting cell injury. Conclusions Combined administration of furosemide and kanamycin sulfate has apparent synergistic ototoxic effect. Although spiral ganglion dam age may not be apparent within a short time period of drug administration, damage to auditory nerve fibers is obvious.