Lymphangiomas are rare benign shlow-growing tumors composed of lymphatic channels. They are generally classified according to the size of their lymph channels as simple, cavernous, and cystic lymphangioma or cystic hygroma. The simple and cavernous types usually occur in the head, neck or axillae. About 75 percent of cystic lymphangioma occur in the neck and 20 percent in the axillae, the remaining 5 percent occur in the mediastinum, omentum, pelvis, groin, spleen, bone, and skin, etc. Purely mediastinal cystic lymphangiomas are very uncommon. We report a case of purely mediastinal cystic lymphangioma confirmed pathologically and treated by operation, along with a review of the literature.