To observe the clinical efficacy of nicorandil for treating the patient with cardiac syndrome X (CSX) and its impact on vascular endothelial function. Methods: A total of 140 CSX patients were randomly divided into 2 groups: Control group, the patients received conventional anti-angina therapy and Nicorandil group, based on conventional anti-angina therapy, the patients received additional oral nicorandil treatment. n=70 in each group. All patients received resting emission computed tomography (ECT) and treadmill exercise ECG stress test (TET). Blood levels of endothelin (ET-1), high-sensitivity C-reactive protein (hs-CRP) and nitric oxide (NO) were examined before and 3 months after treatment. Results: Compared with pre-treatment condition, the attack frequency of angina pectoris and positive rate of ECT were decreased after treatment in both groups, P<0.05; in Nicorandil group, the suspicious positive rate and positive rate of TET were reduced after treatment, P<0.05. Compared with Control group, Nicorandil group had the much lower suspicious positive rate and positive rate of TET after treatment, P<0.05. Blood tests indicated that compared with pre-treatment condition, ET-1 and hs-CRP were decreased, NO was increased after treatment in both groups, all P<0.05; blood levels of ET-1, hs-CRP and NO were different between 2 groups after treatment, all P<0.05. Conclusion: Nicorandil could inhibit inflammatory factors, elevate endothelial function and therefore improve micro vascular angina symptoms, increase exercise tolerance obviously.