Objective : Tarag refers to fermented milk, which has been recognized as daily food of summer in nomadic culture. Also, tarag is cleary defined as a fermented milk product in most of east Asian medical texts. When it comes to tarag-juk described in Korean medical texts, however, there is no definite distinction between milk porridge and tarag-juk. This paper is aimed at finding out whether tarag was merely meaning milk in Joseon. Method : Historical documents of related historical stage, Tibetan and East Asian medical texts, and some cookbooks are mainly consulted, as well as other sources that contains the perception of tarag in Korean history. Result : Tarag is documented as fermented milk in the medical texts of herbs, while tarag-juk is defined as milk porridge in some medical texts in Korea. In one of the Mongolian-Korean dictionary of 18C, milk tea is explained as tarag tea. Conclusion : Although there is not much evidence to back up this conclusion with satisfaction, it would not be to much to say that conception of tarag met some changes from yogurt to boiled milk during Joseon dynasty.