There are abundant records of portents(災異) in Jos?nwangjosillok (『朝鮮王朝實錄』). Generally unusual astronomical and meteorological phenomenons that could not be empirically explained well, and natural disasters such as earthquakes, droughts, deluges and infections were regarded as portents and recorded even though some supernatural phenomenons remained. Especially the amount of records of portents in Jos?nwangjosillok are concentrated in its the 16th century part and this is deeply related to a theory of portents (災異論) discussed actively in the 16th century. A theory of portents played an ambivalent role in a political scene. Tung Chungshu(董仲舒) who systematized the theory as a political ideas of confucianism supported sovereign power of rulers and also imposed a limit, namely portents(災異) to prevent an indefinite extension of the power at the same time. However, after the theory has been used as a real political logic, it has functioned as an idea, which could both reinforce and restrict rulers’ rights. In other words, rulers could prove the fact that they had received a mandate from Heaven (天命) and domination were proper by responding initiatively to portents, and government officials could restrict a despotism of rulers by using a power from Heaven which had higher authority than rulers. The fundamental nature of the theory was harmoniously revealed in a 16th century political scene in Jos?n Dynasty(朝鮮王朝). Infeudation between the king, Jungjong(中宗) and officials that had been stiffened in the reign of Yeonsangun(燕山君) was reorganized after the Restoration(中宗反正), journalism weakened was restarted, and the conflict between the Meritorious Elite (勳舊) and the Neo-Confucian Literati(Sarim,. 士林), who were adversarial each other because of an acceptance of the Neo-Confucian political idea(朱子學 政治論) was occurred in the 16th century. The political environment in 16th century was suitable for a theory of portents spreading out animatedly, which could be utilized widely in a real political scene. Chungjong(中宗) and Myeongjong(明宗) took pushfully part in a discussion of portents to clarify obtainments of a mandate from Heaven and to legitimize his succession to the throne. Opinion seeking policy (Gu-un, 求言) declared frequently in the beginning period of the reign of Chungjong and Myeongjong was produced in responding to portents process for themselves. On the other hand, officials and intellectuals could not merely expand the right to express critical opinions(言權) against King’s policy but also propose a political demand stably through discussing a theory of portents. Moreover, they applied a theory of portents to disseminating the Neo-Confucian political idea by leading a self-examination(恐懼修省) of King which had been a traditional measure to eliminate portents to the Sage Learning for the Ruler(君主聖學論). The theory of portents was, hereby, used to contribute to stabilizing rulers’ rights, reinforcing the right to express opinions, and disseminating the Neo-Confucian political idea. In this way, the theory of portents could have a historical significance in spreading a history of political thought process in the 16th century in Jos?n Dynasty.