Abstract: The study of subjectivity in modern Chinese concentrates on the “subjective quantity” of modern Chinese, that is, a speaker’s subjective evaluation of the deviation of the actual quantity from the supposed one. This thesis argues that the subjectivity of quantity, which is not the same as the subjective quantity, means a speaker’s subjective evaluation of the deviation of the actual comparison quantity in a unit from the potential comparison quantity in a unit. There are two types of the subjectivity of quantity in modern Chinese, namely, the “deviation” of the actual comparison quantity in a unit from the potential comparison quantity in a unit, and the “approaching” of the former to the latter. While the “deviation” mainly concerns the subjectivity of adverbs in syntax, the “approaching” is relative to the subjectivity of optimization in linguistic practice: in an unnatural conversation, for instance, the speakers will choose their subjective expressions according to their information advantage.