Objective : We try to find out the literature and clinical evidences of seasonal formula through the analysis of the addition and subtraction of medical herbs in the formula according to the season. Method : In this study, we analyzed 122 seasonal prescriptions from "Dong-uibogam(東醫寶鑑)", "Bang-yakhappyeon(方藥合編)", "Jeongchijunsueng(證治準繩)", "Dangyesimbeop(丹溪心法)", "Uihakimmun(醫學入門)", "Uihakjeongjeon(醫學正傳)", "Gyeong-akjeonseo(景岳全書)" and "Taepyeonghyeminhwajegukbang(太平惠民和劑局方)". Results : In spring, pungent-warm herbs such as the dried rhizome of cnidium officinale Makino, the dried root of SEdebouriella divaricata (Turcz.) Schischk. are used. In summer, bitter-cold such as the dried root of Scutellaria baicalensis Georgi, the dried rhizome of Coptis chinensis Franch. or pungent herbs such as the dried aerial part of Elsholtzia splendens Nakai, the dried ripe seed of Dolichos lablab L. are added. In fall and winter, pungent-bitter-hot herbs such as the dried ripe fruit of Evodia rutaecarpa Benth., the dried rhirome of Zingiber officinale Rosc. are used. Conclusions : In this paper, we have shown that several medical herbs could be added and subtracted in the formula according to the season because they have the seasonal characteristic Gi or treat seasonal pathogens.