BACKGROUND: The authors proposed that ketogenic diets will produce an increase in the ratio of branched chain amino acids (BCAAs) and aromatic amino acids (BCAAs) in plasma of children who are on the diets. SUBJECTS AND METHOD: A sample of plasma amino acids sample before initiation of fasting and on day 10 of the dietary treatment was obtained in patients with refractory epilepsy who were newly admitted for initiation of ketogenic diet. Plasma amino acids were determined by high performance liquid chromatography equipment. RESULTS: There are 20 patients with refractory epilepsy participating in this study. Outcomes of ketogenic diet therapy were satisfactory. Nineteen cases out of 20 cases had a significantly higher ratio of plasma BCAAs:ARAAs during ketogenic diets than before the diet (P < 0.001). CONCLUSION: The ketogenic diets produced an increased ratio of plasma BCAAs:ARAAs. Whether the increased ratio of plasma BCAAs:ARAAs plays an important role in controlling epilepsy is yet to be elucidated.