Objective To investigate the relationship between lipoprotein associated phospholipase A2 (Lp－PLA2)and atherosclerotic plaque instability in patients with acute coronary syndrome (ACS),and to provide theoretical basis for diagnosis and treatment of ACS.Methods From September 2015 to February 2016,80 patients with ACS in Shidao People's Hospital of Rongcheng were selected as the study group,including 38 cases in unstable angina group(UAP group),24 cases in non ST segment elevation myocardial infarction group (NSTEMI group), 18 cases in ST segment elevation myocardial infarction group(STEMI group).Forty patients with stable angina pectoris (SAP group)and 40 healthy subjects(healthy group)were selected as control group.Each group was collected 8 hours fasting morning blood sample,the levels of Lp－PLA2,C reactive protein(CRP),troponin Ⅰ,and low density lipoprotein were detected,in order to compare the differences among the groups and the correlation between Lp－PLA2 and ACS plaque instability was analyzed.Results The levels of Lp－PLA2,CRP,troponin Ⅰ and low density lipopro-tein in the ACS group were (312.63 ±11.14)ng/mL,(21.98 ±7.83)mg/L,(0.720 ±0.490)μg/L,(174.76 ± 30.82)mg/dL,respectively,which were significantly higher than those of the healthy group [(141.14 ±12.30)ng/mL, (2.38 ±1.68 )mg/L,(0.010 ±0.003 )μg/L,(79.24 ±17.80 )mg/Ml],and stable angina pectoris group [(176.42 ±12.44)ng/mL,(4.22 ±3.68)mg/L,(0.010 ±0.004)μg/L,(96.54 ±19.41)mg/mL].There were statistically significant differences among all groups(F＝3.07,1.99,2.43,3.25,all P＜0.01).The levels of CRP, Lp－PLA2 and cTnI in ACS patients with different types of the STEMI group,NSTEMI group,UAP group had statisti-cally significant differences,which of the STEMI group were higher than those of the NSTEMI group,which of the NSTEMI group were higher than those of the UAP group(F＝5.15,3.47,2.43,all P＜0.05).Correlation analysis showed that the level of Lp－PLA2 was positively correlated with low density lipoprotein(r＝0.625,P＜0.01)and lipoprotein a(r＝0.532,P＜0.01).logistic regression analysis showed that Lp －PLA2 and CRP were significant independent risk factors of ACS,Lp－PLA2(OR＝1.613,95%CI:1.292 －1.992,P＜0.01),CRP(OR＝1.452, 95%CI:1.210-1.782,P＜0.01).Conclusion Lp－PLA2 is independent risk factor of ACS.Lp－PLA2 is involved in the inflammatory reaction of ACS,and is strongly associated with the stability of atherosclerotic plaque.