The most common anterior mediastinal tumors originate from the thymus. Among them, thymic carcinomas occur as an early local invasion and wide spread metastases. However, when squamous cell carcinoma in the thymus or mediastinum is identified, an occult primary lung cancer must be excluded because the histologic types resemble those found more typically in the lung. CD5 and cytokeratin immunohistochemical staining is useful in evaluating biopsy samples from those tumors. Spuamous cell carcinoma of an unknown primary origin in the mediastinum is a rare occurrence and there are only a handful of case reports. Here we describe a case with an anterior mediastinal mass of squamous cell carcinoma with unknown primary origin. A resection of the mediastinal mass without an association with the lung was performed. Immunohistochemical stainings were positive using cytokeratin 13, and negative using CD5 and cytokeratin 7. This was followed by chemotherapy for presured thymic carcinoma.