Background: The no-reflow phenomenon is associated with poor clinical outcomes for patients with acute myocardial infarction (AMI). It may be useful, therefore, to be able to predict which angiographic morphology is at high risk for no-reflow phenomenon after percutaneous coronary intervention (PCI). Materials and Methods: The study population comprised 116 consecutive patients with ST-segment elevated MI who underwent PCI within 7 days of symptom onset. Angiographic no-reflow was defined as TIMI (thrombolysis in myocardial infarction) 0, 1 or 2 flow just after stenting. Preinterventional angiographic parameters including QCA (quantitative coronary analysis), TIMI flow grade, thrombus grade and morphology were analyzed. Thrombus grade was defined as followings; 0:no thrombus; 1:intraluminal haziness; 2:<1/2 vessel diameter; 3:0.5~2 vessel diameter; 4:>2 vessel diameter; 5:total occlusion. Results: Angiographic no-reflow was seen in 41 (35.3%) of 116 AMI patients. No-reflow group showed larger reference vessel size (3.41짹0.43 vs. 3.15짹0.43, p=0.004), smaller minimal lumen diameter (0.18짹0.29 vs. 0.37짹0.42, p=0.02) and higher incidence of preinterventional TIMI 0 flow (48.8% vs. 20.3%, p=0.001) than reflow group. Lesion diffuseness and irregularity was similar in both groups. Cutoff pattern of thrombus (48.8% vs. 20.2%, p<0.001) was frequent in no-reflow group, however frequencies of filling defect pattern (22.0% vs. 21.3%) and intraluminal haziness pattern (29.3% vs. 33.3%) were similar in both groups. No-reflow group also showed higher incidence of thrombus grade 5 (51.2% vs. 20.0%, p<0.001). Multivariate logistic regression analysis showed that reference vessel size (p=0.003; odds ratio 6.93; 95% CI 1.902 to 25.213) and thrombus grade (p=0.024; odds ratio 3.60 95% CI 1.182 to10.941) are independent predictive factors of no-reflow phenomenon after PCI of AMI. Conclusion: Large vessel size and thrombus burden are at high risk for no-reflow after reperfusion of AMI. These findings provide clinically useful information in selection of potential candidates for adjunctive therapy with PCI.