Thymolipoma is a rare benign mediastinal tumor, composed of mature fatty and thymic tissues. A 9-year-old boy was referred with a one-month history of neck swelling. Preoperative computed tomography scan and fine needle aspiration biopsy suggested thymolipoma. Despite it being rare, thymolipoma should be considered in the differential diagnosis of mediastinal tumors. Characteristics of its clinical feature and radiological findings that can differentiated it from other mediastinal tumors are discussed with a review of the literatures.