The relationship between hyperlipoproteinemia and sensorineural hearing loss has been studied by means of guinea pig models with hypercholesterolemia. However, these observations of the inner ear using guinea pig models have been limited to a short time. By using a golden hamster model with hypercholes terolemia, I was able to observe the inner ear for a long time. Two-month-old hamsters were fed a hyperlipid diet consisting of standard chow supplemented with 3% cholesterol and 15% cattle fat for 30, 60, 90, 120, and over 150 days. Six-month-old hamsters were fed the hyperlipid diet for 30 days. Then the animals were examined for auditory dysfunction and morphological changes in the cochlea. Biochemical findings in the serum showed hyperlipoproteinemia, especially hypercholesterolemia. Regarding auditory dysfunction, the threshold change in the auditory brainstem response (ABR) was mild. Scanning and transmission electron microscopic revealed many protrusions toward the endolymphatic space on the surface of the marginal cells of the stria vascularis. Vascular degeneration of the marginal cells and intermediate cells of the stria vascularis was also observed. In addition, protrusions containing a lysozome structure consisting of outer piller cells were observed on the organ of Corti. These results with experimental hamsters fed a hyperlipid diet indicate that such a diet may induce functional changes in the cochlea such as auditory dysfunction with the occurrence in hypercholesterolemia.