Background: The aim of this study was to examine relationship between the parameters of pulmonary function and the severity of coronary artery disease (CAD) in chronic obstructive lung disease patients. Materials and Methods: Four hundred and twenty four patients with ischemic heart diseases who underwent coronary angiography were studied. The demographic characteristics and medical history of the patients were obtained from their medical records.The severity of COPD was determined according to the Global Initiative for Chronic Obstructive Lung Disease. In addition, the severity of CAD was quantified by SYNTAX scoring . Results: Eighty-eight (21.2%), 270 (65.1%), 52 (12.5%), and 5 (1.2%) of the patients had the grade 1, 2, 3, or 4 COPD, respectively. In addition, 46 (11.1%), 319 (76.9%), and 50 (12.0%) of them had low, intermediate, and high CAD, respectively. A statistically significant relationship was observed between the severity of COPD and the severity of CAD. Significant relationships were found between age, sex, BMI, LDL, EF, and systolic pressure of pulmonary artery with the severity of COPD. The odds of higher CAD in females were 1.849 times higher than male patients. In addition, the odds of high CAD in the patients with grade 1 or 2 COPD were 0.006 and 0.068 times of the patients with grades 3 and 4 COPD, respectively . Conclusions: The findings of the present study indicate that the parameters of pulmonary function and the severity of CAD are associated with the severity of COPD.