Purpose: We report the case of a 12-year-old female patient who visited a Korean medicine clinic to treat functional dyspepsia. In addition, we aim to contribute to the accumulation of clinical cases of Gamchosasim-tang in the Shanghanlun. Method: We analyzed whether Gamchosasim-tang contributed to the improvement of functional dyspepsia. In addition, we examined how the clinical expression of ‘痞’ was revealed in the case. Results: The total period of herbal medication was 90 days. During this period, the patient’s chief complaints including nausea before sleep, epigastric discomfort, loss of appetite, and sleep difficulties have improved. Meanwhile side effects were not observed. ‘痞’ was manifested in this patient’s behavior of refusing food such as eating small meals and picky eating. Conclusion: In this case, Gamchosasim-tang contributed to the improvement of functional dyspepsia. When prescribing Gamchosasim-tang in Provision 158 of Shanghanlun, it is advisable to consider whether there is a behavior of refusing food, such as eating small meals and picky eating.