Abstract: Objective：To investigate serum complement 1q (C1q) levels in the patients with coronary artery disease (CAD), and evaluate its clinical values in predicting and discriminating acute coronary syndrome (ACS) and stable coronary artery disease (SCAD). Methods：A total of 52 ACS patients, 66 SCAD patients and 54 healthy controls were enrolled in this study. Their serum C1q and oxidized low-density lipoprotein (ox-LDL) levels were detected by an immune turbidimetric method and an enzyme linked immunosorbent assay, respectively. Their serum total cholesterol, triglyceride, highdensity lipoprotein cholesterol and low-density lipoprotein cholesterol levels were also determined. Then, the Gensini scores in CAD patients were calculated, and the clinical values of C1q in predicting and discriminating ACS and SCAD were evaluated by stepwise multiple linear regression analysis and Logistic regression analysis. Results：Serum C1q and ox-LDL levels in ACS (C1q:t=4.405, P<0.001; ox-LDL: Z=5.941, P<0.001) and SCAD (C1q: t=2.320, P=0.022; ox-LDL: Z=4.119, P<0.001) patients were significantly higher than those in healthy controls. Moreover, serum C1q (t=2.344, P=0.021) and ox-LDL (Z=2.166, P=0.030) levels in ACS patients were significantly higher than that in SCAD patients. Serum C1q levels were positively correlated with serum ox-LDL (r=0.246, P=0.028) and TG (r=0.232, P=0.002) levels and Gensini scores (r=0.341, P=0.020) in ACS patients. The stepwise multiple regression analysis showed that serum ox-LDL levels were still independently correlated with serum C1q levels in ACS patients (β=0.676, P=0.045, adjusted R²=0.380) after adjusting for age, gender and other biochemical markers. The Logistic regression analysis showed that the increased serum C1q and ox-LDL levels were closely related to the occurrence of ACS (C1q: OR=1.05, 95%CI=1.03-1.08, P<0.001; ox-LDL: OR=1.18, 95%CI=1.08-1.29, P<0.001) and SCAD (C1q: OR=1.04, 95%CI=1.01-1.06, P=0.003; ox-LDL: OR=1.11, 95%CI=1.03-1.18,P=0.004), and that they could discriminate ACS and SCAD (C1q: OR=1.01, 95%CI=1.00-1.03, P=0.022; ox-LDL: OR=1.06, 95%CI=1.01-1.12, P=0.023). Conclusion：Serum C1q levels increase significantly in CAD patients, and that of ACS patients is significantly higher than SCAD patients. In ACS patients, serum C1q levels are independently correlated with ox-LDL levels. Serum C1q levels may be served as a novel biomarker for the prediction and discrimination of ACS and SCAD.