The ototoxic drugs were injected into the middle ear cavity and abdominal cavity of guinea pig. 4 mg Gentamycin was injected into the middle ear cavity for successive 10 days. The neurosensory epithelium of vestibular apparatus was severely damaged. During this degenerative process the various changes of rigidity, fusing, balloon-like changes of sensory cilia were observed by using scanning electron microscope. In the groups of intra peritoneal injection of streptomycin, similar results were recognized. But the groups which were applied with Gentamycin into middle ear cavity showed stronger acute changes than the intra peritoneal injection groups. And also new findings of otoconial degeneration were seen through intra peritoneal streptomycin injection.