As part of research on the Chinese subjective decrement markers, this study is aimed at analyzing the combinatorial aspect and semantic characteristic of them through a synchronic and diachronic research especially into ‘不怎么’ and ‘不那么’, both of which are of profound significance for expressions denoting the subjective decrement. By means of doing so, the work seeks to understand the background, and further to clarify the grammaticalization process whereby they are used as markers showing the subjective decrement. “Quantity is an important category with which humans perceive, understand and make expressions of the world”, and “the quantitative category of the linguistic world is divided into objective quantity and subjective one”. The subjective quantity is defined as that which comes to have subjectivity due to the speaker's subjective evaluation of the objective quantity, and is usually divided into large and small one. Research related to the subjective quantity has attracted the attention of many scholars and there have been remarkable achievements made with regard to it even in Chinese language studies. However, there has been a limitation, on the other hand, that most of the studies have focused only on the syntax, semantics and pragmatics of expressions denoting the large subjective quantity and small one. What needs to be paid attention to, in this respect, is that the Chinese language also has expressions for the subjective decrement such as ‘不怎么’ and ‘不那么’ in addition to those for the large and small subjective quantity. For all that, few researchers have observed and analyzed them from the perspective of the subjective quantity. For such a reason, this study considers ‘不怎么’ and ‘不那么’ to be the subjective decrement markers most of all, analyzing the combinatorial aspect and semantic characteristic of and the difference between them through a synchronic research. Then, another analysis of their degrees of lexicalization is conducted through a diachronic research into their semantic expansions and frequency increases based on the examination of their periodic examples. The work, in the last analysis, deduces their grammaticalization processes along with the background analysis of how meanings of the subjective decrement have come to be generated in them despite the fact that they have not in other interrogatives or demonstratives.