Adenoid cystic carcinoma is an uncommon histologic variant of adenocarcinoma which usually arises from the salivary, lacrimal, or other exocrine glands. Characteristics of adenoid cystic carcinoma are its potential for extending long distance submucosally and for perineural invasion. It grows slowly and may have a prolonged course before diagnosis and after treatment. Recently, we have experienced 2 cases of adenoid cystic carcinoma arising from main bronchus and trachea. One case was 58 years old female patient. Her symptoms were productive cough with dyspnea. She has been history of shortness of breath, wheezing and cough during 4 years, which was initially diagnosed as bronchial asthma. The tumor was located on the left main stem bronchus which was obstructed the lumen nearly complete, by CT demonstration. Tissue diagnosis was confirmed as adenoid cystic carcinoma by bronchoscopic biopsy. The patient underwent radiation to relieve a bronchial stenosis caused by her tumor. The patient has remained well and is asymptomatic without evidence of clinical recurrence. The other case was 25 year old female. She complained shortness of breath and inspiratory difficulty during sleep. The tumor was located in upper trachea, which protruded from the posterior wall of the trachea and obstructed the lumen nearly complete, by CT demonstration. Tissue diagnosis was confirmed as adenocystic carcinoma by rigid bronchoscopic biopsy. The patient was underwent operation for removal of the mass and received radiotherapy. The patient has remained well are following up now.