A case of invasive thymoma with hypogammaglobulinemia showing endobronchial growth is presented. A 63-year-old man was admitted for evaluation of a left hilar mass. A biopsy specimen obtained from the intraluminal mass, which occluded the left upper division bronchus, was highly suggestive of thymoma. The laboratory tests were almost normal except for hypogammaglobulinemia. The tumor was resected with the left upper lobe. Most of the tumor invaded the left upper lobe, and grew into the bronchi. The case was diagnosed histologically as invasive thymoma spreading within the bronchial lumen.