Objectives : This study aims at exposing interaction between socio-cultural influence on medicine, and the strong quest for rational explanation concerning the evil-spirit(鬼邪) related disease, namely Sasu(邪?), in medical history. Methods : In order to apprehend the change of perception, Chinese medical classics referring directly to Sasu(邪?), as well as Korean medical classics from Joseon dynasty were reviewed. Results : In Chinese medical texts, discriminating pseudo-sasu(類似邪?) from evil-spirit related sasu had been one of the main concerns. And Chinese were more inclined to specify treatment plan for pseudo-sasu than handling evil spirits. On the contrary, Korean medical texts show common interests in eliminating evil spirits throughout Joseon dynasty. Conclusions : Since medicine is under the influence of socio-cultural condition, it cannot escape from the epistemology of corresponding society. Evil-spirit related disease therefore could remain within the sphere of medical discussion until very recently. If we observe the disease under the frame of culture, we not only can obtain broader view on dynamic nature of medical conceptions, but also gain better insight to understand medical classics.