Background: Some patients with non-ST elevation myocardial infarction (NSTEMI) showed total occlusion of infarct related artery (IRA) and may have clinical benefits from early invasive treatments. The aim of this study was to investigate the predictors of total occlusion of IRA in patients with NSTEMI before coronary angiography. Methods: A total of 205 consecutive patients with NSTEMI (63.3짹10.5 years, 123 males) who admitted and underwent coronary angiogram from 2005 April to 2006 December at Chonnam National University Hospital were divided into two groups; group I (total occlusion of IRA: n=62, 61.1짹13.3 years, 42 males) and group II (patent IRA: n=143, 64.2짹11.3 years, 81 males). Clinical, biochemical, and echocardiographic parameters at admission were compared between the groups. Results: Total occlusion of IRA in patients with NSTEMI was observed in 62 (30.2%) patients and most frequently in left circumflex coronary artery. Predictive factors for total occlusion according to multivariate analysis were prolonged duration of continuous chest pain (OR:9.67, 95% CI:1.59~80.6, p=0.03), higher level of creatine kinase-MB fraction (CK-MB) (OR:5.35, 95% CI:1.31~90.0, p=0.035) and fibrinogen (OR:6.73, 95% CI:1.48~50.2, p=0.043), and higher number of leads with ST depression in ECG (OR:4.78, 95% CI:1.22~41.9, p=0.048). Conclusions: Total occlusion of IRA in acute NSTEMI is associated with long duration of chest pain, high levels of CK-MB and fibrinogen, and ST changes in multiple ECG leads.