Aim To investigate whether the plasma plasminogen activator inhibitor-1(PAI-1) activity and gene polymorphism played a pathogenetic role in acute coronary syndrome(ACS). Methods 106 patients suffering from acute coronary syndrome(ACS) and 98 subjects,who were suffering from stable coronary heart disease(SCHD),and 60 normal controls were recruited.The 4G/5G allele polymorphism were genotyped by using polymerase chain reaction technique,while plasma activity assayed by enzyme linked immunosorbent assay. Results The plasma PAI-1 activity level in the ACS group(18.0±2.9 kAU/L) was significantly higher than that in the SCHD group(16.8±2.7 kAU/L) and in the control group(16.2±2.8 kAU/L;p<0.01 or p<0.005).The frequency of 4G/4G allele homozygous in the ACS group(49.1%) was significantly higher than that in the SCHD group(28.6%) and in the control group(26.7%;p<0.05).The plasma PAI-1 activity level was statistically higher in 4G allele homozygous than those in 4G/5G heterozygous and 5G homozygous(p<0.05). Conclusions There may be a link between the plasma PAI-1 activity and it's 4G/5G genotype.Elevated plasma PAI-1 activity and essentially 4G allele homozygous genotype might be the major risk factors of ACS.