Abstract: Objective :To analyze the relationship between chronic obstructive pulmonary disease (COPD) and the risk of lung cancer. Methods :The analysis was based on the data of a case control study conducted during the period from 1999 to 2001 in Xi'an, China, and was evaluated by the odds ratio (OR). Results :The patients with COPD had an increased risk of lung cancer, OR=2.25 for Bron- chins and OR=2.33 for Emphysema. When FEV, was lower than 70%, the risk of lung cancer increased (OR=2.28). Conclusions :The risk of lung cancer increases in the patients with a history of COPD, and the impairment of lung function is suggested to increase the risk of lung cancer.