Lack of historical records causes some difficulties in the historical studies of ancient Korea. It is the same case as that of the history of medicine. We imagine what the situation of medicine was like in ancient Korea with a bit of historical records. In ancient times, medicine had very close relation with religions. In ancient Korea, it had very close relation with Buddhism. According to {Sam Kuk Sa Ki and {Sam Kuk Yu Sa buddhists monks treated patients with the religious rituals. In this article, the authors would like to present a record which had been unnoticed until now. It is the commentary of Wonhyo on a certain Buddhistic cannon called {Kum Kwang Myung Kyung. A chapter of this cannon is on the theory of medicine, causes of diseases and treatments. We can presume Wonhyo's knowledge of medicine at that time through his commentary on this chapter.