Objective:To assess the effect of G894T polymorphism in exon 7 of the endothelial nitric oxide synthase gene(eNOS)on the development of acute coronary syndromes(ACS). Methods:By means of Polymerase Chain Reaction and Restriction Fragment Length Polymorphism,G894T Polymorphism of eNOS was detected in 260 patients with ACS(120 with acute MI and 140 with unstable angina) and 248 subjects excluded CHD by coronary angiography. Results:Genotypes GT+TT and T allele frequency in ACS group were significant higher than those in control group(23.46%vs 9.27%,14.42%vs 5.24%)(P < 0.01). There was no significant difference in genotypes GT+TT between AMI subgroup and UAP subgroup(20.83% vs 25.71%,P > 0.05). That did not correlate with the number of coronary vessels diseased in patients with ACS. Conclusion:The T allele of eNOS gene might be associated with ACS and a risk genetic marker of CHD evolution in ACS. But that is not related to the severity of coronary diseased.