Background Many studies have shown that the serum uric acid (SUA) level is one of the cardiovascular risk factors.The aim of the study is to evaluate the relationship between SUA levels and the severity of coronary artery disease (CAD) assessed by angiography and the Syntax score in patients with obstructive CAD.Methods Participants who visited our hospital for a coronary angiography,from December 2007 to September 2012,were eligible for this analysis.SUA and other blood parameters after at least 12-hour fast were determined.First,the patients were divided into tertiles according to their Syntax scores (low Syntax score group:Syntax score ≤10.0; moderate Syntax score group:10.0 ＜Syntax score ≤18.0; high Syntax score group:Syntax score ＞18.0).Second,to clarify the association between SUA levels and major adverse cardiovascular events (MACEs),all patients were divided into two subgroups on the basis of SUA levels.The cutoff value of SUA was defined by diagnostic criteria of hyperuricemia.Patients were separated into normal SUA group (n=251,with SUA ＜416 μmol/L for men and SUA ＜357 μmol/L for women) and high SUA group (n=96,with SUA ≥416 μmol/L for men and SUA ≥357 tμmol/L for women).All participants were followed for a mean of 22.0 months (1-75 months,interquartile range:28 months) for major adverse cardiovascular events (MACEs),including all-cause death,recurrent nonfatal myocardial infarction (re-MI) and recurrent percutaneous coronary intervention (re-PCI).Results A total of 347 patients were registered for the study.The SUA levels in the high Syntax score group were significantly higher than that of the moderate Syntax score group and the low Syntax score group ((392.3±81.6) μmol/L vs.(329.9±71.0) μmol/L,P ＜0.001; (392.3±81.6) μmol/L vs.(311.4±64.7) μmol/L,P ＜0.001).The SUA level was positively correlated not only with the Syntax score (r=0.421,P ＜0.001; 95％ CI:0.333-0.512),but also with the number of diseased vessels (t=0.298,P ＜0.001; 95％ CI:0.194-0.396).After multiple linear regression analysis,SUA levels were identified to be independently correlated with a high Syntax score (B=0.033,95％ CI 0.023-0.042,P ＜0.001).Compared with the normal SUA subgroup,the high SUA subgroup tended to have a higher Syntax score (19.9±8.7 vs.13.6±7.5,P ＜0.001) and more multi-vessel disease (70.8％ vs.46.6％,P ＜0.001).Follow-up data showed a higher incidence of MACE in the high SUA subgroup (20.8％ vs.6.0％,P ＜0.001).Binary Logistic regression analysis indicated that the elevated SUA can predict the long-term prognosis of patients with obstructive CAD (OR=2.968,95％ CI 1.256-7.011,P=0.013).KaplanMeier analysis showed a significantly lower event-free survival rate in patients with high SUA levels than in the normal SUA subgroup (79.2％ vs.94.0％,Log rank=17.645,P ＜0.001).Conclusions SUA levels were independently associated with the severity of CAD in patients with obstructive CAD.An elevated SUA is associated with cardiovascular events and may be useful as a biomarker of the severity of CAD.