Background: The beneficial effects of B-blocker on early and long-term outcome after acute myocardial infarction were shown before the introduction of thrombolysis and angiotensin-converting-enzyme inhibitors. Benefits have been demonstrated for patients with and without concomitant fibrinolytic therapy. These benefits occur at a risk of provocation of CHF or complete heart block and the development of cardiogenic shock. So the use of B-blockers in eligible patients is substantially lower than would be expected from the convincingly positive results. We investigated the use of B-blocker and the efficacy of B-blocker on the mortality in patients with AMI (KAMI registry patients). Methods: In a multicenter trial (4517 patients with a proven acute myocardial infarction), 4236 patients with the information of hospital medications were enrolled. 2803 (66.3%) were administered with B-blocker and 1427 patients (33.7%) were not administered with B-blocker. Results: All-cause hospital mortality was lower in B-blocker group (2.0% versus 9.6%, p<0.001). But the B-blocker group included younger (mean age 62.9 years versus 64.9 years, 0.001) patients and the higher proportion of low risk patients (higher left ventricular ejection fraction, higher mean systolic blood pressure, and Killip class I and class II patients). The other medical history (Hypertension, Diabetes, Hyperlipidemia, Smoking) were similar between the two groups. Conclusion: The treatment with B-blocker in the patients of KAMI registry was underutilized especially in the high risk patients, even though the beneficial effect on the mortality.