The purpose of this study is to examine the characteristics of five Joseon dynasty annotations of the Daodejing, a sutra of Daoism. The Joseon dynasty was a country that adopted Zhu Xi’s Neo-Confucianism as its state ideology; as a result, Daoism and Buddhism were considered heresies. In order to investigate how the Daodejing, a book of heresy, was understood in Joseon, this article will focus on how Zhu Xi was cited in the annotations of the Daodejing. The way Zhu Xi was cited in these books can simultaneously reveal the annotators’ thoughts about both Laozi and Zhu Xi. Two conclusions were drawn from this study. First, the annotators from the Joseon dynasty understood dao as a metaphysical system of Neo-Confucianism and Zhouyi 周易 (Book of Changes). In so doing, they attempted to ascertain the common characteristics between Confucianism and Daoism. Secondly, there were two different purposes in the citations of Zhu Xi in the annotations of the Daodejing: to seek new alternative systems of thought using Zhu Xi’s authority and to defend the academic conformity of Neo-Confucianism by reinterpreting Laozi’s thoughts in the perspective of Neo-Confucianism.