There are four kinds of formulas for purging the liver to cure its sthenic syndrome based on the types of preparation formulas : Sagan-tang, Saganhwan, Saseem-san and Saganeum. Another formula called Sacheonghwan, Sacheong-tang and Sacheong-san is to purge the green colour of liver. There are 38 kinds of Sagan-tang, 2 kinds of Saganhwan, 29 kinds of Sagan-san, 5 kinds of Saganeum, 4 kinds of Sacheonghwan, 3 kinds of Sacheong-tang and 1 kind of Sacheong-san. Combination of herbal medicines, carried out in formulas for purging the liver, consists of various kinds depending on medical scientists' personal experience in medical treatment without any general principles, which makes it difficult to apply it to clinical use. The objectives of this study lie in theoretical establishment of Sagan-tang for curing the sthenic syndrome of liver through analyzing the component medicines and combination principles of Hyeongok's Sagan-tang, and furthermore, maximizing the clinical use of Sagan-tang. This study analyzed the component medicines and combination principles of Hyeongok's Sagan-tang based on the theory for properties and tastes of herbal medicines from the ${\ulcorner}$Yellow Emperor's Canon of Internal Medicine${\lrcorner}$, the theory for principal herbal medicine, assistant herbal medicine, adjuvant herbal medicine, dispatcher herbal medicine, and the five elements doctrine. Hyeongok's Sagan-tang is an odd prescription, composed of 7 kinds of ingredients : No.1 Radix Paeoniae (2don;7.5 g), No.2 Fructus Chaenomelis (1don;3.75 g), No.3 Radix Rehmanniae (1don), No.4 Folium Phyllostachydis Henonis (1don), No.5 Radix Bupleuri (1don), No.6 Radix Scutellariae (1don), and No.7 Radix Glycyrrhizae (1don). There are three methods for curing the sthenic syndrome of liver according to the five elements doctrine : purging the liver, purging the heart and invigorating the lung. In the case of taste purgation, two herbal medicines with sour taste, Radix Paeoniae and Fructus Chaenomelis, are combined into the principal and assistant herbal medicine, respectively. For property purgation, two herbal medicines with the cool property, Radix Bupleuri and Radix Scutellariae, are combined into adjuvant herbal medicines. Both sweet and cold herbal medicines, Radix Rehmanniae and Folium Phyllostachydis Henonis, are combined into adjuvant herbal medicines. Sour herbal medicines, Radix Paeoniae and Fructus Chaenomelis, were combined to invigorate the lung. Cool herbal medicines, Radix Bupleuri and Radix Scutellariae, were combined to invigorate the lung and to purge the liver. In addition, Radix Glycyrrhizae are combined as dispatcher herbal medicine, harmonizing all the herbal medicines composing the formula. First, to cure the sthenic syndrome of the liver, the methods of purging the liver and the heart, and invigorating the lung should be used according to the five elements doctrine. Secondly, herbal medicines appropriate for those treatment methods should be chosen according to the theory for properties and tastes of herbal medicine and thirdly, the combination of those herbal medicines should be carried out according to the theory for principal herbal medicine, assistant herbal medicine, adjuvant herbal medicine, dispatcher herbal medicine. As a good example, Hyeongok's Sagan-tang is combined according to the above theories.