Limitations of histologic study about the hair cells in the inner ear have been caused by the facts that the membranous labyrinth lies in the hard center petrous bone, has an extremely complex structure, and has the characteristic of early post-mortem degeneration. In this study, the author performed in-vivo fixation with 1.5% osmium tetroxide and post-fixation with modified Karnovsky's fixative in the normal guinea pigs. The crista ampullaris were embedded with immunobed and cut with the thickness of 2μm by Reichert-Jung Supercut. The mid-portions of each crista ampullaris were collected and stained with hematoxylin-eosin. The mounted 180 sides form 10 guinea pigs were analyzed under light microscope with the system of Quantiment-520 image analyzer. The results are as follows : 1) The ratio of sensory hair cell and supporting cell is 1 : 1.6. The supporting cells are more compactly located in the central portion. 2) The ratio of type I and type II sensory hair cell is 2.9 : 1. The ratio is 4.0 : 1 in the central portion and 2.2 : 1 in the peripheral portion. 3) The area of epithelial layer is 53.3% of the total. The area of sensory hair cells is 62.2% of the epithelial layer. 4) The area of nerve fibers is 9.0% of the stromal layer. The results could be a basic knowledge for further studies about the functional aspect of the crista ampullaris and the pathophysiology of various ototoxic effects.