A female in her 40s was admitted with an abnormal shadow on chest X-ray. A chest computed tomography (CT) revealed an anterior mediastinal cystic mass with calcification. We suspected the tumor to be a teratoma, and surgery was performed. The tumor was connected with the thymus, and did not infiltrate to the surrounding tissues. Macroscopically, the cyst was multiloculated with fibrous walls. Microscopically, thymic tissue was noted in the cyst wall, with neither thymic epithelial tumor nor teratoma. The cyst wall contained collagen fibers, cholesterol clefts, and calcification. Based on these findings, the tumor was diagnosed as multilocular thymic cyst with calcification.