To elucidate the ultrastructural change of corneal epithelium co-cultured with herpes simplex virus (HSV), the corneal epithelium of 3 rabbits was excised and cultivated in culture media. After 7 days, the Kos strain of herpes simplex virus was inoculated in the cultured cornea epithelium until cytopathic effect was occurred. It was fixed in the solution of 3% glutaraldehyde and examined with electronmicroscope. In co-cultured cells, the intercellular spaces had increased and microvilli were seen prominently. The virus particles that initiated the infection by fusing the viral envelope with the plasma membrane were also seen. The nuclear degeneration in an infected cell was prominent. The nuclear membrane was folded markedly, and the chromatin was degraded, condensed and displaced toward the nuclear membrane. Numerous viral particles and inclusion bodies were present in the nuclei. These findings suggest that the infectious process of herpes simplex virus in the human corneal epithelium may occur in a similar way. This result would be helpful in understanding the pathogenesis of herpes simplex epithelial keratitis.