We present a case of mucous gland adenoma arising from the main bronchus of the lower lobe of the left lung in terms of clinicopathologic, immunohistochemical, and ultrastructural aspects as well as review of related literatures. The patient, a 31-year-old female, was admitted to Catholic University Medical College Hospital with complaints of coughing and purulent sputum for about seven years. The chest CT showed a severely calcified tumor in the left lower lobe of the lung. Grossly, the calcified tumor arising from the main bronchus protruded into the lumen and showed bronchiectasis of the lower lobe and atelectasis of the upper lobe of the lung. The tumor was pale brown-gray and sharply circumscribed and showed some small cystic spaces filled with mucoid material. Microscopically, most of the tumor showed dystrophic calcification. The growth pattern of the tumor is composed of cysts, tubules, and glands lined by cytologically bland columnar, cuboidal, or flattened mucus secreting cells. Electron micrograph of tumor cells showed some round or oval mucous granules measuring 0.5-1.8 micrometer.