Purpose: Early primary coronary angioplasty (PCI) has been considered the "gold standard" in the treatment of acute ST segment elevation myocardial infarction (STEMI). ST segment elevation resolution in electrocardiogram correlates with reperfusion, and known as a strong predictor of the final outcome. The aim of this study is to evaluate the early clinical characteristics and biochemical markers for predicting ST segment resolution after primary PCI. Methods: From January 2006 to June 2007, 116 consecutive patients admitted with STEMI at Kyung Hee University Medical center and Kyung Hee East-West Neo Medical center, among them 113 patients treated by primary PCI. Median door to balloon time was 138 짹 66.8 minutes. They were divided into three groups according to the ST segment resolution, as originally described by Schroder et al: Complete (���70% depression of the elevated ST-segment, n=45, 58.6짹14.1 years, male 82%), Partial (30% to 70%, n=38, 61.4짹 12.4 years, male 71%), and Incomplete (<30%, n=30, 66.4짹13.6 years, male 70%). Symptom-to-balloon times (classified as <2 hour, 2 to 4 hour, 4 to 6 hour, >6 hour), door-to-balloon times (<90minute, 90 to 120 minute, 120 to 150 minute, 150 to 180 minute, >180 minute), initial ejection fraction (EF, <35%, 35 to 50%, >50%), biochemical markers, pre-, and post-Thrombolysis in Myocardial Infarction (TIMI) flow grade were evaluated. Results: Symptom-to-balloon times, door-to-balloon times were significantly prolonged in incomplete ST segment resolution group (P < 0.01). Increased initial EF, and post-TIMI flow grade were in the correlation with complete ST segment resolution (P < 0.01). Using a multivariate logistic regression model, increased wall motion score index, N-terminal pro BNP, troponin I, and high sensitivity CRP were associated with incomplete ST segment resolution. 6 month-MACEs (major adverse cardiac events) were also increased in incomplete group (30%) compared with complete (4%) and partial (3%) groups (P < 0.01). Conclusions: Variable clinical and laboratory markers indicating extensive myocardial injury and delayed treatment due to any reason were associated with incomplete ST segment resolution.