Objectives : The concept of hidden Yin in summer by Zhu Danxi deals with the relationship between summer heat disease and hidden yin inside of human body. This paper attempts to ponder upon the clinical issues around which the discussions regarding the topic unfolded, and upon the texts on which the doctors of the discussions based their opinions. Methods : First, Danxi`s argument as discussed in Gezhiyulun is analyzed to find out his understandings of clinical issues and his textual sources on which he based his new perspective. Moreover, the prescriptions that Danxi thought was problematic and the concept of hidden yin as it existed before the time of Danxi are reviewed, and these findings are used understand Zhangjingyue`s ground of criticism against Danxi. Lastly, this paper contemplates how these opposing opinions may be helpful to the general principles of medical theories. Results & Conclusions : There was a trend before the time of Danxi of abusing drugs as prescription based on warm-heat, understanding that a human body has yin-cold during summer. However, Danxi brought forth a new concept of yin deficiency in order to correct people`s misunderstanding. Despite his effort, Zhangjingyue and other doctors contemporary to Danxi emphasized on one hand that human body is placed on a state of external heat inside the cold, and on the another, criticized Danxi of failing to fully understand the principle of "Abandon the time and follow the symptoms", a principle which asserts that the cold and warm of medicine should be decided by the symptom itself and not by the season. The value of these contradicting assertions seems to hold true even to this day because it helps us understand that the principles of "Counting Season as a Treatment Factor" and "Abandon the time and follow the symptoms" could be applied with balance in conjunction with each other.