Thymoma is the most common anterior mediastinal tumor in adults. Rarely, it is presented as the anterior neck mass, commonly located in the anterolateral aspect of the neck or adjacent to the thyroid. We experienced two cases of fine needle aspiration cytology of thymoma, mimicking thyroid mass. The first case was an ectopoic cervical thymoma in a 31-year-old female. The fine needle aspiration cytology was misinterpreted as reactive hyperplasia of lymph node. But the histologic diagnosis was thymoma, predominantly lymphocytic type. The second case was an invasive thymoma in a 66-year-old female, who complained a large anterior neck mass. The fine needle aspiration cytology revealed biphasic population of some clusters of epithelial cells and scattered lymphocytes. The cytologic diagnosis was thymoma and was confirmed as invasive thymoma after the biopsy. Therefore, when the cytologic feature of anterior neck mass shows the both lymphocyte and epithelial component, the differential diagnosis should Include the possibility of thymoma.