Recently published reports on Korea's medieval mummies have been regarded as an invaluable source for studies into the physical characteristics of medieval Koreans. However, even though the mummified tissues have been investigated histologically on various previous occasions, there are many unanswered questions relating to their tissue preservation. The aim of this study was to obtain new data on the ultramicroscopic characteristics of the mummified skin of a fifteenth-century mummy found recently in Daejeon--one of the oldest ever found in Korea. Electron microscopy revealed that much of the epidermis had decayed; what remained of the dermis was filled with collagen fibres and melanin granules or invading bacterial spores present within the mummified epidermis. Considering the histological characteristics shared by naturally formed mummies in different parts of the world, we concluded that the ultramicroscopic patterns of the Daejeon mummy were more comparable with those naturally formed mummies than with artificially formed ones. This is the first full description of the morphological characteristics of the skin collected from this recently found medieval mummy from Daejeon, South Korea.