Background: Leukocyte count is closely associated with the risk of coronary artery disease (CAD). Levels of leukocyte subpopulations in patients with CAD, however, remain largely unknown. Methods: In this study, we compared the distributions and counts of 16 leukocyte subpopulations between 40 patients with CAD and 40 healthy controls using the CytoDiff flow cytometric system. Results: Our results demonstrated significant increases in the frequencies and counts of all monocytes, immature granulocytes, and B-lymphocytes in patients with CAD, suggesting that the levels of these leukocyte subpopulations may serve as potential biomarkers for diagnosis of CAD. By contrast, the levels of cytotoxic T/natural killer lymphocytes were markedly decreased in patients with CAD. In addition, the levels of T/natural killer lymphocytes, noncytotoxic T-lymphocytes, mature neutrophils, total neutrophils, eosinophils, basophils, and T-cell blasts in CAD patients with elevated levels of cardiac troponin I (cTnI), an independent indicator for poor prognosis in CAD, were significantly different from those in CAD patients with normal levels of cTnI. These data may help in the screening for biomarkers to discriminate between stable and unstable patients with CAD. Conclusions: Collectively, our results provide a detailed distribution profile of leukocyte subpopulations in patients with CAD and suggest their possible clinical application in predicting the risk and severity of CAD.