Yosimasu Nangai (吉益南涯) is son of Yoshimasu Todo (吉益東洞), an eminent figure of traditional Japanese medicine. He wrote many medical books including Ihan(醫範) and Kigetusuiyakucho(氣血水藥徵), which contain core thoughts of Nangai. This study analyzed Ihan(醫範) and Kigetusuiyakucho(氣血水藥徵) to figure out Nangai’s explanation in depth. Conclusion is as follows. He was influenced by his father’s theory that all diseases come from one toxin but there were many differences in his theory. Also influences of qi-blood-phlegm stasis theory(氣血痰鬱論) established by Zhudanxi(朱丹溪) are apparent in several aspects. Consequently he established his own body fluid pathology called qi-blood-fluid theory(氣血水論).