Objective To study the ultrastrueture of vestibular membrane of the cochlea in guineapig. Methods The vestibular membrane in guineapig's cochlea was observed under scanning electron microscope. Results The mesothelium on the perilymphatic side was formed by a single thin layer which was intermittently discontinuous. Microvilli were few on the surface of mesothelial cells. Nuclei of the cells were large and oval in shape. A single layer of polygonal epithelial cells were observed on the endolymphatical side. The irregular polygonal epithelial cells were round and oval in shape. Many microvilli were found on this side. The junction between these cells was very tight. Conclusion The vestibular membrane is a barrier between the scala media and scala vestibule and might play a role in ion and fluid homeostasis