From the 10th and 11th centuries, the Mencius philosophy gradually attracted interests among Chinese scholars. Many Confucian scholars started to annotate Mencius philosophy while others had critiques on it. During the Southern Song Dynasty, Zhu Xi who is a great scholar wrote extensive commentaries for the ”Four Books,” and later they were widely accepted as the standard commentaries. As a result, the Mengzi is classified into one of the Confucian Classics. The influence of the Four Books upon the Confucianism is so large that they served as the basis of the civil service examinations in Ming and Qing Dynasties. On the other hand, due to the great contributions of the Cheng-Zhu school, Neo-Confucianism was intensively studies by scholars, and became one of the most important philosophies at that time. However, during the 17th and 18th centuries, the Confucian scholars reconsidered essence of the Confucianism and thought people who study the Confucianism should emphasized on the Confucius and Mencius philosophies instead of the Neo-Confucianism. Therefore critiques on the Neo-Confucianism began to increase, and one of the most significant exponents is Dai Zhen.Dai Zhen who was born in Qing Dynasty severely criticized the Cheng-Zhu school of the Neo-Confucianism. He was insistent on the conventional Confucianism, and wanted to liberate Mencius philosophy which was tortured by politics over the past hundreds of years. The objective of this article is to understand why Dai Zhen rewrote the commentaries of the Mengzi by the following steps. Let us start from backgrounds of the academic activities of Mencius philosophy during Ming and Qing Dynasties followed by realizing the methodologies Dai Zhen used to interpret Mencius philosophy. Then we reconsidered whether the commentaries by Dai Zhen are consistent with Mengzi itself, or new understandings of it. Finally, the new path to Mencius philosophy created by Dai Zhen will be highlighted.