We report a case of a 72-year-old woman who died of primary lung clear cell adenocarcinoma. She was an active smoker, but with no other significant previous medical abnormalities. She visited our hospital with complaining of hemoptysis lasting for a month. Her sputum production and coughing had also increased. Chest X-ray films showed obstructive pneumonia in the left lower lobe. Chest computed tomography (CT) showed a tumor shadow and collapsed portion in the left hilar area. Sputum cytology and further diagnostic tests revealed stage IV lung adenocarcinoma. Chemotherapy with carboplatin and paclitaxel was initiated, but no improvement was obtained. She died from progressive cancer invasion into the airway. An autopsy revealed that more than 90% of the cancer cells were clear cells. These cancer calls were positive for PAS and occasionally showed Alcian blue-positive intracytoplasmic mucin and glandular structures. They were immunocytochemically stained with cytokeratin 7 but not with cytokeratin 20. According to previous reports in the literature, cases of primary lung clear cell adenocarcinoma are very rare.