Background and Purpose. The role of antibody against oxidized low-density lipoprotein (Ab-ox-LDL) in acute myocardial infarction (AMI) and coronary artery disease (CAD) has not been fully elucidated. This study investigated the relationship between Ab-ox-LDL titers and the extent of coronary atherosclerosis, and determined the clinical significance of this antibody in AMI. Methods. A total of 70 patients with significant coronary atherosclerosis demonstrated by coronary angiography were recruited. These patients were divided into AMI (n = 33; mean age, 63 yr; 29 men) and chronic stable CAD (n = 37; mean age, 62 yr; 30 men) groups. Serum Ab-ox-LDL was measured using an enzyme-linked immunosorbent assay. The extent of coronary atherosclerosis was assessed by an angiographic diffuse score system. Results. In all patients, Ab-ox-LDL was significantly correlated with white blood cell count (r = 0.309; p = 0.009), but not with lipid profile or the diffuse score. Ab-ox-LDL (422.0 +/- 60.4 vs. 263.8 +/- 30.2 U/L; p = 0.018), white blood cell count (9,742 457 vs. 7,211 +/- 327/mm(3); p < 0.001), and C-reactive protein (10.5 +/- 3.1 vs. 2.9 +/- 0.5 mg/L; p = 0.022) were significantly higher in patients with AMI than in those with chronic CAD. Peak creatine kinase concentration was significantly correlated with Ab-ox-LDL (r = 0.499; p = 0.003) among patients with AMI. Conclusion: Ab-ox-LDL is higher in patients with AMI and is correlated with myocardial damage to a greater degree than with the severity of coronary atherosclerosis and lipid profiles.