To investigate the efficacy and safety of tolvaptan (TLV) in patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH)at Kyoto-Katsura Hospital, a retrospective chart review of TLV dosage, duration, change in serum sodium concentration from baseline to Day 14 after the initial TLV administration, and side effects was performed. In 27 patients (mean age: 75.4 years), the main causes of SIADH were drugs (33.3％) and small cell lung cancer (SCLC) (33.3％). Patients administered TLV received a mean starting dose of 3.97 mg (SD 1.45) and mean daily dose of 4.10 mg (SD 1.65). The maximum TLV dosage did not exceed 7.5 mg. The treatment duration of TLV required for serum sodium improvement (Na ≥ 135 mEq/L) was 5.91 days (SD 3.33) in all patients. TLV was administrated for 13.44 days (SD 1.57) to maintain the serum sodium in SCLC patients. Concomitant sodium load (≥ 100 mEq orally or intravenously) did not significantly affect the duration of improvement in hyponatremia [sodium load vs load-free: 7.1 days (SD 3.4) vs 5.3 days (SD 3.1), P = 0.24]. The side effects were dry mouth (11.1％) and hypernatremia (3.7％). In conclusion, we confirmed the effectiveness and safety of TLV for hyponatremia of SIADH at low doses for 14 days. TLV may improve the quality of life in patients with loaded sodium intake, and could be used in the longer run to treat SCLC with a permanent antidiuretic hormone production.