The purpose of this study is to more clearly reveal the meaning(strengths and shortcomings) of the moral subject that can be derived from Dasan(茶山)'s concept of ‘sim(心)’. To this purpose, this study adopted a method of comparing sim concepts of Dasan and Yangming(陽明). The conclusions of this study are as follows. First, Dasan greatly emphasized the mental aspect of sim. Because of sim, which has the power to judge and choose, human beings possess characteristics as ‘moral subjects’ that are different from non-human beings. And that responsibility for judgment and choice must be borne by me as a moral subject. Second, Dasan defined the relationship between dosim(道心) and insim(人心) as confrontational and dichotomous, and saw that dosim was the manifestation of a moral tendency unique to human beings. However, this moral tendency is granted by sangje(上帝), and since dosim cannot be separate from sangje, sim is not trusted by itself. Third, moral tendency and dosim are only in human beings, and humans as moral subjects are responsible enough to provide conditions for the nature of other beings to be well implemented, but no further responsibility is morally requested.