To investigate the expression of inducible nitric oxide synthase (iNOS) in the hydropic cochlea of guinea pigs, the experiment consisted of two groups: normal control group and experimental group. The hydropic animal model was established by destroying the endolymphatic sac. The expression of iNOS in the hydropic cochlea was examined by immunohistochemistry. The results showed that the expression of iNOS in the hydropic cochlea was positive. The expression of iNOS in the area of stria vascularis and spiral ganglion cells was much stronger. It is suggested that nitric oxide is involved in the pathophysiology of cochlear dysfunction in hydropic cochlea.