Neiging Medicine(內經醫學) based on Yin-Yang and Five elements was the main stream of Korea Traditional Medicine until the end of 19th century. And the establishment of Sasang Constitutional medicine. In this paper, author proved that the Yin-Yang of Sasang Constitutional Medicine was different from that of Neiging Medicine and that explained the Yin-Yang of Sasang Constitutional Medicine as our own medicine. After considering the philosophical and medical background of Sasang Constitutional Medicine, and author researched the Yin-Yang of ontology, structure, function, symptoms in Sasang Constitutional Medicine. Also we compared this with that of Neiging medicine. The results were as follows 1. Neiging Medicine was based on the Yin-Yang and Five elements centering on the nature and Sasang joy, and pleasure centering on the human. 2. The ontology of Sasang Constitutional Medicine were the mind as a unitary substance, the mind and body as a dual substance, and affair, mind, body, and objects as a four substance which were the basic theory of philosophy. 3. Sasang Constitutional Medicine explained social phenomenon with a four substancial structure consisted of affairs, mind, body, and objects, a complex four substancial structure consisted of heaves, human, nature and order, and a three dimension structure including time. 4. On the other hand Neiging Medicine recognized seven emotions as five emotions, Sasang Constitutional Medicine recognized seven emotions as qi, nature, and emotions which consisted of sorrow, anger, joy, and pleasure. The qi had an effect on internal and external part of body and the nature and the emotion had an effect on the upward and downward of body. 5. It was taked great importance to control the up and down balance and the internal and external balance in Sasang Constitutional Medicine instead of reinforcing and reducting method of Neiging Medicine. 6. The Yin-Yang of Korean Traditional Medicine developed centering on the human from centering on the nature and Sasang Constitutional Medicine was a practical medicine compared with Neiging Medicine.