This study deals with the ornamental ridge-end Roof-end tiles called ‘chimi’ which were produced in the North-South States Period to adorn each end of the main ridge of a roof. It is thought that these ridge-end Roof-end tiles began to be made in the mid to late fourth century. However, in Korea there have been few studies on ridge-end Roof-end tiles largely due to a lack of examples that can provide detailed information on their form. This study deals with the development of ridge-end tiles in the Unified Silla and Balhae kingdoms based on the examples excavated so far and on other historical materials related with the architecture of both kingdoms. It has not been easy, however, to obtain detailed dates of their origins or their development because the original tiles, being over one meter in height, were rather large, and because little is known about the locations where they were discovered. So far, twenty-one ridge-end tiles have been excavated at the sites of the capital cities of the two kingdoms. These surviving artifacts are largely divided into two types, each of which is then subdivided into four types according to the designs decorating the main part and the central vertical band. The main difference between the first two types is related with their development from the undecorated tiles of the Three Kingdoms Period into the tiles of the later period, which characteristically feature cintamani or semi-spherical decorations around their central vertical band and floral patterns on their main part. Types 2 to 4 include tiles whose shape developed from a design representing the head of a beast. It must be admitted that this study’s discussion on the development of ornamental ridge-end tiles is somewhat limited due to a lack of examples to be studied and accordingly is subject to leaps of logic. It is expected, therefore, that more extensive and accurate research on the subject will follow if future excavations yield more reliable information about the tiles’ origins.