Objective To investigate the role of red cell distribution width ( RDW) in coronary artery diseases patients complicated with obstructive sleep apnea-hypopnea syndrome ( OSAHS) . Methods 134 coronary artery diseases patients who had at least one-vessel disease confirmed by coronary angiography were investigated by polysomnography for OSAHS. The patients were classified according to theapneahypopnea index(AHI) . The level of RDW, triglyceride, cholesterol, high density lipoprotein, low density lipoprotein, hemoglobin, white blood cells and hematocritwere measured. The receiver operating characteristic curve was drawn to predict the moderate-severe OSAHS in coronary artery diseases patients according to RDW value. Results When 134 coronary artery diseases patients were classified into a control group and an OSAHS group according to the AHI, the level of RDW in two groups was not significantly different [ ( 13.44 ±1.30) % vs. ( 13.12 ±0.92) % , P gt; 0.05] . When 134 coronary artery diseases patients were classified into a control and mild OSAHS group and a moderate-severe OSAHS group according to the AHI, the level of RDW in two groups was significantly different [ ( 13.07 ±0.94) vs. ( 14.02 ±1.41) % , P lt; 0.05] . And no difference was found in hemoglobin, triglyceride, cholesterol, high density lipoprotein, low density lipoprotein, platelet, and hematocrit between two groups. The ROC curve analysis revealed that the area under ROC curve was 0.748 ( 0.523-0.972) , and the best cut-off for moderate-severe OSAHS was 13.95% with sensitivity of 71.43% and specificity of 82.98% . Conclusion RDW may be a useful and simple tool to predict moderate-severe OSAHS in coronary artery diseases patients.