Background: As an acute phase protein, α1-antitrypsin (AAT) has been extensively studied in acute coronary syndrome, but it is unclear whether a relationship exists between AAT and stable angina pectoris (SAP).The purpose of the present study was to investigate the association between AAT plasma levels and SAP.Methods: Overall, 103 SAP patients diagnosed by coronary angiography and clinical manifestations and 118 control subjects matched for age and gender were enrolled in this case-control study.Plasma levels of AAT, high-sensitivity C-reactive protein (hsCRP), lipid profiles and other clinical parameters were assayed for all participants.The severity of coronary lesions was evaluated based on the Gensini score (GS) assessed by coronary angiography.Results: Positively correlated with the GS (r =0.564, P < 0.001), the plasma AAT level in the SAP group was significantly higher than that in the control group (142.08 ± 19.61 mg/dl vs.125.50 ± 19.67 mg/dl, P < 0.001).The plasma AAT level was an independent predictor for both SAP (odds ratio [OR] =1.037, 95% confidence interval [CI]: 1.020-1.054, P < 0.001) and a high GS (OR =1.087,95% CI: 1.051-1.124, P < 0.001) in a multivariate logistic regression model.In the receiver operating characteristic curve analysis,plasma AAT level was found to have a larger area under the curve (AUC) for predicting a high GS (AUC =0.858, 95% CI: 0.788-0.929,P < 0.001) than that of hsCRP (AUC =0.665, 95% CI: 0.557-0.773, P =0.006;Z =2.9363, P < 0.001), with an optimal cut-off value of 137.85 mg/dl (sensitivity: 94.3%, specificity: 68.2%).Conclusions: Plasma AAT levels correlate with both the presence and severity of coronary stenosis in patients with SAP, suggesting that it could be a potential predictive marker of severe stenosis in SAP patients.