Aim To investigate the serum level of cluster of differentiation 137 (CD137) in patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS) and evaluate its prognostic value in patients with NSTE-ACS.Methods 122 hospitalized patients were divided into two groups:NSTE-ACS group (n＝93) and control group (n＝29).According to GRACE score, NSTE-ACS group was divided into three subgroups:low-risk group, medium-risk group and high-risk group. Cardiac troponin I (cTnI), brain natriuretic peptide (BNP) and other biochemical indicators were measured in each group. The serum level of CD137 was determined by enzyme-linked immunosorbent assay. Major adverse cardiac events (MACE) were followed up for 1 year in all patients. Receiver operating characteristic curve (ROC) was used to evaluate the value of serum CD137 level in mid-term prognosis of NSTE-ACS patients. Results Compared with the control group, the serum CD137 level increased significantly in each subgroup of NSTE-ACS group (P＜0.01). Among the subgroups of NSTE-ACS group, the serum CD137 level in high-risk group was significantly higher than that in low-risk group and medium-risk group (P＜0.05). Serum CD137 level was positively correlated with GRACE score (r＝0.867, P＜0.01), and it was also positively correlated with cTnI and BNP levels (r value was 0.942 and 0.945, respectively, both P＜0.01). The incidence of MACE in NSTE-ACS group was significantly higher than that in control group in one year (P＜0.01), and serum CD137 level was positively correlated with the incidence of MACE (r＝0.324, P＜0.01). The area under the ROC curve of CD137 predicting mid-term MACE in NSTE-ACS patients was 0.847 (95%CI 0.718-0.918, P＜0.01), and the sensitivity and specificity were 80.0% and 79.4% respectively. Conclusion Detection of serum CD137 level is helpful for risk stratification of patients with NSTE-ACS and has certain clinical value for prognosis judgement of patients with NSTE-ACS.