Hypercalcemia due to hyperparathyroidism is rarely associated with acute pancreatitis. But, the relationship between hypercalcemia and pancreatitis still remains controvesial. Ectopic parathyroid adenoma with cystic change is one of the rare causes of hyperparathyroidism, and is usually located in neck and mediastinum. We report a case of mediastinal parathyroid adenoma with cystic change associated with acute pancreatitis. A 54-year-old male presented with epigastric pain for 3 days. The serum calcium, phosphate, elastase were 16.8mg/dL, 1.1 mg/dL, 2772.0 ng/mL respectively and his parathyroid hormone level in serum was 651.84 pg/mL. Chest CT showed a mediastinal mass with well defined inhomogenously enhanced density located between SVC and aorta. The patient was diagnosed to hyperparathyroidism with acute pancreatitis due to mediastinal parathyroid adenoma with cystic change, and was surgically removed. The surgical biopsy showed parathyroid adenoma with cystic change. After operation his general condition was improved and serum calcium, phosphate, amylase, lipase level were normalized.