To avoid fluctuation of the serum lithium concentration (CLi), sodium chloride (NaCl) intake was regulated in oral alimentation. A 62-year-old woman was hospitalized and orally administered 400 mg of lithium carbonate a day to treat her mania. Her CLi was found to be 0.75-0.81 mEq/L. Vomiting made it difficult for the patient to ingest meals orally, and therefore parenteral nutrition with additional oral intake of protein-fortified food was initiated. On day 22, parenteral nutrition was switched to oral alimentation to enable oral intake of food. The total NaCl equivalent amount was decreased to 1.2 g/d, and the CLi increased to 1.15 mEq/L on day 26. Oral alimentation with semi-solid food blended in a mixer was immediately initiated. Although the total NaCl equivalent amount was increased to 4.5-5.0 g/d, her CLi remained high at 1.14-1.17 mEq/L on days 33 and 49, respectively. We investigated oral administration of NaCl (1.8 g/d) on day 52. The total NaCl equivalent amount was increased to 6.3-6.8 g/d, and the CLi decreased to 1.08-0.97 mEq/L on days 63 and 104, respectively. After the start of the orally administered NaCl, her diet was changed to a completely blended diet on day 125. The total NaCl equivalent amount was increased to 9.0-14.5 g/d, and the CLi decreased to 0.53 mEq/L on day 152; therefore, the oral administration of NaCl was discontinued on day 166. The CLi was found to be 0.70-0.85 mEq/L on days 176 and 220.