A case of uric acid stone (4×2.5 cm) of the left renal pelvis, was demonstrated by sonography, excretory urography and abdominal computer tomography. The urine pH of the patient tended to be acidic. Two months after the start of alkalization of the patient’s urine by U-Citra (potassium citrate and citric acid), both urolithiasis and the symptoms disappeared completely. The amount of undissociated urinary uric acid decreased (UA: 612 mg/day). Potassium citrate delivered an alkali load, urinary alkalization and citraturic response and retarded the propensity for the crystallization of calcium salts and uric acid by decreasing the urinary saturation and/or increasing the inhibitor activity. The result demonstrated that alkalization of urine by potassium citrate is an effective treatment for uric acid stone.