Background: The no-reflow phenomenon after primary percutaneous coronary intervention (PCI) is associated with greater infarct size, worse functional recovery, and higher incidence of complication in acute myocardial infarction (AMI). The aim of this study was to assess the relation between apolipoprotein B/A-I ratio and angiographic no-reflow phenomenon and its long-term influence on major adverse cardiac events (MACE). Methods: Between October 2005 to April 2007, we measured serum Apo B and Apo A-I level in 664 consecutive AMI patients (62.5짹12.3 years, 478 men) on admission and before PCI. Results: The subjects were divided into 2 groups at the approximately 75th percentile Apo B/Apo A-I value: group I had an Apo B/Apo A-I ratio ���1 and group II <1. The baseline clinical characteristics between the group I (n=488) and group II (n=176) showed no significant difference. In logistic regression analysis, the Apo B/Apo A-I ratio ���1 [odd ratio (OR) 6.671, 95% confidence interval (CI) 1.888-23.571, p=0.003] was an independent predictor for the no-reflow phenomenon along with previous statin therapy (OR 5.758, 95% CI 1.273-26.051, p=0.023), while high glucose level (OR 0.990, 95% CI 0.981-0.999, p=0.036), high LDL-cholesterol level (OR 0.977, 95% CI 0.961-0.994, p=0.007) and high BMI (OR 0.851, 95% CI 0.738-0.982, p=0.027) have shown the trends of lowering the no-reflow phenomenon. Kaplan-Meier analysis showed no significant difference in MACE-free survival rate between two groups (p=0.514 by Log-rank test). In Cox proportional hazard regression analysis, the family history of AMI [relative risk (RR) 4.495, 95% confidence interval (CI) 1.069-18.895, p=0.040], bare metal stent (BMS) implantation (RR 2.488, 95% CI 1.070-5.781, p=0.034, regional wall motion score (RWMS) (RR 1.113, 95% CI 1.006-1.233, p=0.039) and high hsCRP (RR 1.200, 95% CI 1.071-1.344, p=0.002) were predictors for long-term MACE, but the Apo B/Apo A-I ratio has failed to be an independent predictor (RR 3.615, 95% CI 0.978-13.354, p=0.054). Conclusion: Apo B/A-I ratio is a strong predictor for the development of no-reflow phenomenon during PCI in patients with AMI, although it has failed to predict long-term adverse outcomes.