Carcinosarcoma is an uncommon pulmonary malignancy characterized by carcinomatous parenchyma and sarcomatous stroma. Pulmonary carcinosarcoma represented about 1% of the resected lung tumors. The predominant clinical features are productive cough, chest pain, dyspnea, hemoptysis, bronchiectasis, and atelectasis, but alternate atelectasis is rare. We report a case of pulmonary carcinosarcoma associated with alternate atelectasis of the right upper and lower lobe.