Milk-alkali syndrome (MAS), a triad of hypercalcemia, metabolic alkalosis, and renal failure, is associated with ingestion of large amounts of calcium and absorbable alkali. MAS is the third most common cause of hypercalcemia in hospital, after primary hyperparathyroidism and malignant neoplasm. MAS is not often reported in the Korean literature. We describe MAS secondary to intake of calcium citrate for the treatment of osteoporosis with thoracic spine compression fracture. A 70-year-old man presented to our hospital with a 1-week history of general weakness and lethargy. He was found with acute kidney injury (serum creatinine, 4.6 mg/dL), hypercalcemia (total calcium, 14.8 mg/dL), and alkalosis. Laboratory evaluation excluded both hyperparathyroidism and malignancy. Mental status and serum calcium level was normalized within a week after proper hydration and intravenous administration of furosemide. However, he developed aspiration pneumonia, pseudomembranous colitis, and sepsis with multi-organ failure. Despite intensive treatment including inotropics, mechanical ventilation, and renal replacement therapy, he expired with no signs of renal recovery on the 28th hospital day.