The main objective of this study is to explore the characteristics of the early Southern Song Cheng learning (chengxue 程學) tradition, which remains a missing link in Neo-Confucian history, through examining the scholarship of Zhang Jiucheng 張九成 (1092-1159). Zhang’s scholarship is characterized by two prominent features. Zhang was a prolific commentator of Confucian classics, covering the Zhongyong, the Mencius, and the Book of Documents, to name a few. Albeit diversely formulated, this single principle mainly concerns how to grasp the inner morality of human nature (or the inner mind) and put it into practice. This practical sphere of self-cultivation prescribed by Zhang shows high affinity to the Buddhist counterparts, which invited severe criticism from Zhu Xi and later Neo-Confucian scholars. Nonetheless, the rise of Zhang Jiucheng in the intellectual community of the early Southern Song sheds light on how the Cheng learning tradition was understood at that time. Philosophically, Zhang reconciled the conceptual contradiction between the naturalness of the inner mind (or human nature) and the artificiality of human efforts by separating the realm of spontaneous manifestation of the inner mind from the realm of subsequent intentional actions. However, this approach leads to another philosophical problem, namely a dichotomization of the mind (or human nature) into the object to seek and the agent of seeking it, a problem which Zhu Xi later brought to light and addressed.