Background Acute non-ST segment elevation myocardial infarction (NSTEMI) is usually managed according to an early invasive strategy for patients with high clinical risks. However, clinical trials on early intervention in Korea are evidently limited. Based on the data enrolled in the KAMIR, authors analyzed the prognosis according to the timing of PCI in patients with acute NSTEMI in Korea. Methods 2458 patients of high risk NSTEMI in KAMIR from Jan. 2005 to Dec. 2007 were classified by the time interval from the onset of chest pain to the PCI (Group I < 24 hr, Group II 24-48 hr, Group III > 48hr). The clinical outcomes were evaluated based on major adverse cardiac events (MACE) during the follow up period. Results Of the 2471 patients enrolled, 329 patients experienced MACE; MI, rePCI, CABG, cardiac death and non-cardiac death. The incidence of MACE in the group I was 113(15.1%), the group II 83(14.4%) and the group III 132(11.6%), accordingly. The group I showed higher incidence of MACE than the group III, with statistical significance(p=0.008, Multivariable adjusted harzard ratio 0.64, [95% CI, 0.45-0.9]). The group II had lower incidence of MACE than the group I, but without statistic significance(p=0.18, Multivariable adjusted harzard ratio 0.77, [95% CI, 0.51-1.14]). Conclusion In patients with NSTEMI, the incidence of MACE was higher when PCI performed ithin 24hours of symptom onset, which is statically significant. Therefore, limited early PCI should be considered in NSTEMI patients.