Backgroud: The first on-line registration of Korea Acute Myocardial Infarction patients (KAMIR) has been carried out throughout 40 primary percutaneous coronary intervention (PCI) centers in Korea with support of Korean Circulation Society since Nov 2005. Methods: Between Nov 2005 and June 2006, 1445 acute non-ST segment elevation myocardial infarction (NSTEMI) patients (mean age = 65.1짹13.1 years, 942 males) were enrolled in KAMIR. The treatment strategy of NSTEMI was categorized into conservative treatment (group I) and PCI treatment (group II). PCI group was further catergorized into early invasive PCI (group IIa) and elective PCI (group IIb). Initial clinical status [symbolized into Basal Clinical Status (BCC) which is the summation of risk factor numbers those are composed of pain, dyspnea, cardiogenic shock, pulmonary edema, creatine kinase-MB, Troponin-I], coronary artery disease risk factors, in-hospital mortality, ICU admission days, complication rate were compared between two groups. And mortality rate according to the initial medications was compared. Results: Group I had higher mortality compared with that of group II (6.6% vs.0.9%, p<0.001). Diabetes mellitus and past history of ischemic heart disease were higher in group I than those of group II (36.9% vs. 29.8%, p<0.001; 29.4% vs.19.0%, p=0.008, respectively). Other coronary risk factors rate, BCC score, ICU admission days, complication rate were similar between group I and II. Between group IIa and IIb, there was no difference in mortality, coronary artery risk factors rate, BCC, ICU admission days and complication rate. The patients with initial treatment of beta blockers had a lower mortality compared with the patients without beta-blockers (41.5% vs. 56.9%, p=0.036). Other initial medications with angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and statins had similar mortality rate between the patients with and without treatment of those drugs. Conclusions: Initial conservative treatment of acute NSTEMI patients has higher mortality than that of the patients with PCI treatment. Intial beta-blocker treatment decreases the mortality rate.