This study seeks to investigate the differences between the mind philosophy (simhak) of Donghak and that of Confucianism. Suun’s writings frequently include phrases that resemble the terminology of Confucianism, which was the dominant intellectual tradition at the time. Perhaps as a result, some scholars well-versed in Confucian thought have occasionally misinterpreted Donghak—despite its identity as the unparalleled Mugeuk Daedo (Great Way of the Infinite)—as a derivative branch within the Confucian tradition. However, significant differences exist between the mind philosophy (simhak) of Donghak and that of Confucianism. To begin with, Donghak’s philosophy of mind (simhak) begins with the mental principle (simbeop) of ‘O-sim is Yeo-sim’ (吾心卽 汝心), wherein O-sim is identified with Cheon-sim (the Heavenly Mind), and Yeo-sim is identified with In-sim (the human mind). This study examines the view that O-sim, identified as Cheonsim (the Heavenly Mind), is the mind of Sangje (the Lord on High) and serves as the active agent of the Holy Spirit’s work. In particular, through the teachings of Uiam, this study examines the claim that Donghak’s mind philosophy (simhak) encompasses the full cycle of spiritual activity—conception (胞胎), birth (誕 生), and life (生活)—as reflected in the statement: ‘The activity of spirituality began; [conception] the determination of spirit gave rise to the organization of all things; [birth] and through the organization of all things, the manifestation of spirit reappeared. [life] Next, the mind philosophy (simhak) of Confucianism is traced to the transmission of the phrase Yunjipgweoljung (允執厥中) by Emperor Yao, which was later expanded by Emperor Shun into the sixteen-character mind principle: ‘Insim yu wi, dosim yu mi, yujeong yuil, yunjipgweoljung’ (人心惟危 道心惟微 惟精 惟一 允執厥中), adding three key concepts to the original. This study examines the view that Yujeong (惟精) refers to discerning between the human mind (insim) and the moral mind (dosim) so that they do not become confused, while Yuil (惟一) signifies maintaining constancy in the Way of the Mean (jungyong). It is through the practice of yujeong and yuil that one is able to properly enact the Way of the Mean in everyday life. Finally, this study briefly investigates the differences between the mind philosophies (simhak) of Donghak and Confucianism by examining selected passages from Suun’s writings that explicitly engage in comparison with Confucian ideas. In conclusion, this study argues that the mind philosophy (simhak) of Donghak can be understood as a life-centered moral philosophy, one that transcends the human mind (insim) and embraces the Heavenly Mind (cheon-sim)—the source of life—encompassing the full cycle of conception, birth, and lived experience. The simhak of Confucianism is shown to be a relational moral philosophy that emphasizes maintaining the Mean (jungyong) throughout human life and social conduct. Through this comparative examination, the study highlights the significant differences between the mind philosophies of Donghak and Confucianism.