During the Joseon Dynasty, medicinal foods derived fromherbs were often more effective than traditional medicines. Inaddition, the royal family of theJoseon Dynasty believed that foods could be used as various disease treatments. Grainbasedfoods, especially medicinal porridges (藥粥), were most frequently used for diet therapy. We investigated various typesof diet-related diseases suffered by King Injo (仁祖) as well ashow the diseases were treated using medicinal porridges basedon information in the SeungjeongwonIlgi (承政院日記), which is the daily record of the Royal Secretariat of the JoseonDynasty. This study examined the SeungjeongwonIlgi of King Injo from his1st year (1623) to 27th year (1649) on awebsitedatabase maintained by the National Institute of Korean History. According to the records, King Injo suffered from severediarrhea several times due mainly to febrile disease (煩熱症) as well asabdominal dropsy (脹滿) throughout his entire life.Major diseases affecting King Injo were dueto his unhealthy eating habits and psychological factors. For treatment, royaldoctors prescribed around 15 medicinal porridges, including nelumbo (seed) porridge (Yeonja-juk), milk porridge (Tarakjuk),Chinese dioscorea porridge (Sanyak-juk), mungbean porridge (Nokdu-juk), perilla seed porridge (Imja-juk), adzukibeanporridge (Pat-juk), soybean porridge (Kong-juk), Korean-leek porridge (Buchu-juk), and so on, in addition to othermedical treatments. Diet therapy using medicinal porridges has been usedthroughout history since the Joseon Dynastyperiod. However, knowledge of traditional diet therapy and medicinal porridges used bymonarchs in the Joseon Dynastyis insufficient. Therefore, in-depth study is needed to understand the theory of traditional medicinal foods as well as exploretheir application to patients in the context ofmodern medicine.