Medical science is an area of study that focuses on maintaining health and treating disease. However, modern medicine focuses on treating disease and neglects methodology of maintaining health. Although the definition of heal this defined by the World Health Organization (WHO) and as the concept of harmonizing Yin and Yang in Korean medicine, there is no specific details regarding the definition. Thus, the following conclusion was obtained after the concept of health is viewed through Yin-Yang(陰陽), Vital Essence(精), Qi(氣), and Healthy Person(平人). Although Yin and Yang have opposite properties, they work very closely, maintaining the overall balance and harmony. Secondly, Vin and Yang would each function by the effects of one another, and the body could maintain normal physiological activities through this function. Thirdly, it maintains normal physiological state through the ascending Kidney-Water and descending Heart-Yang(水升火降). Fourthly, Vital Essence is divided into the congenital Essence(先天之精) and the acquired Essence(後天之精) in which the former is related with reproduction and the latter, nourishing. Fifthly, Qi is resistant to pathogens and related with the physique so that Qi and physique should be balanced. Sixthly, Healthy Person is the state where the exchange of Qi-Blood is active.