Objective To study the relationship between the level of serum leptin and the degree of coronary stenosis in patients with coronary artery disease and evaluate their correlations. Methods Twenty patients with stable angina pectoris (stable angina pectoris group ), 26 patients with unstable angina pectoris (unstable angina pectoris group ), and 20 patients with symptom of angina pectoris but without coronary artery disease (control group) were involved in this study, all of whom were diagnosed by coronary arteriography.The levels of serum leptin in the three groups were detected. Results The level of serum leptin in unstable angina pectoris group [(10.39 ± 8.09) μg/L] was significantly higher than that in stable angina pectoris group [(7.65 ±4.46) μg/L] and control group[(3.93 ±2.66) μg/L](P< 0.01). In stable angina pectoris group and unstable angina pectoris group, the lower the angiography TIMI grading, the higher the level of serum leptin. But in the same angiography TIMI grading,the level of serum leptin in two groups had no significant difference. The level of serum leptin in unstable angina pectoris group and stable angina pectoris group had positive correlation with Gensini scores and angiography TIMI grading (r = 0.654,0.542, P < 0.05;r = 0.466,0.518, P < 0.05 ). Conclusions The level of serum leptin is significantly higher in coronary artery disease patients and especially in unstable angina pectoris patients. The level of serum leptin has positive correlation with the degree of coronary disease, the extent of myocardial ischemia, the quantity of stenosis and blood stream of coronary artery.