Micronodular thymoma with lymphoid stroma (MNT) is an extremely rare tumor and has not been reported in Korea. Herein, we report a case of MNT diagnosed in a 75 year-old male. The mass was incidentally identified on thoracic computer tomography (CT) during work-up for a cardiac mass. The resected thymic mass was ovoid and solid measuring 3.5×3 cm in size and showed homogenously white tan, solid and firm cut surface. Microscopically, the tumor had a thin fibrous capsule except small foci of invasion to thymic adipose tissue, and consisted of characteristic multiple discrete epithelial nodules in abundant lymphoid stroma. The epithelial nests anastomosed each other, forming a vague cord-like structure. The cells in the epithelial nests were bland, spindle to oval shape with relatively abundant cytoplasm, slightly vesicular chromatin and one definite nucleolus. The lymphoid stroma contained prominent germinal centers. No evidence of recurrence or metastasis has been found within 4 years of surgery. (J Lung Cancer 2011;10(1):56 ? 58)