Background and Objectives : Current guidelines recommend an early invasive strategy for patients with non-ST segment elevation myocardial infarction (NSTEMI). However, there are many debates still remained about the timing of revascularization in patients with NSTEMI. To analyze the clinical efficacy of the timing of revascularization, we compared the in-hospital clinical outcome of NSTEMI patients between early and selective invasive therapeutic groups in Korea Acute Myocardial Infarction Registry (KAMIR). Subjects and Methods : Between Nov. 2005 and Apr. 2007, 2762 acute NSTEMI patients (mean age = 64.6짹12.8 years, 1847 males) were enrolled in KAMIR. The therapeutic strategy of NSTEMI was categorized into early invasive treatment (within 48 hours, Group I: 63.1짹13.1 years, 1085 males) and selective invasive treatment (Group II: 66.5짹12.1 years, 762 males). Initial clinical status and in-hospital mortality, morbidity rate were compared between two groups. And, in-hospital outcome were also compared between two groups according to each Thrombolysis In Myocardial Infarction (TIMI) risk score. Results : There were significant differences in mortality and morbidity rate between the groups (6.5% vs. 10.3%, p<0.001). According to TIMI risk score, there were no significant differences or mortality and morbidity in low to moderate risk patients (5.3% vs. 7.8%, p=0.123 in risk score 0-2, 6.4% vs. 8.7%, p=0.139 in risk score 3-4), but significant differences in high risk patients (9.0% vs. 17.3%, p=0.003 in risk score 5-7). And early invasive treatment was more effective in patients with old age, diabetes, male patients, elevated troponin I level (RR=1.64, 2.15, 1.91, 1.85 respectively). Conclusions : Early invasive treatment improves a hospital outcome in high-risk NSTEMI patients. Use of abciximab, low ejection fraction, high Killip class, high TIMI risk score and old age are predictive factors in-hospital mortality and morbidity.