Objectives: It has been shown that metabolic syndrome is associated with poor short-term outcome and poor long-term survival in patients with acute myocardial infarction. We aimed to investigate the effect of metabolic syndrome on ST segment resolution in patients received thrombolytic therapy for acute myocardial infarction.Materials and methods: We retrospectively analyzed 161 patients, who were admitted to our clinics with acute ST-elevated-myocardial infarction and received thrombolytic therapy within 12 hours of chest pain. Metabolic syndrome was diagnosed according to National Cholesterol Education Program Adult Treatment Panel III criteria. Resolution of ST segment elevation was assessed on the baseline and 90-minute electrocardiograms. ST segment resolution ≥70% was defined as complete resolution.Results: Metabolic syndrome was found in 56.5% of patients. The proportion of patients with metabolic syndrome who achieved complete ST segment resolution after thrombolysis was significantly lower than that of patients without metabolic syndrome (32.9% versus 58.6%, p=0.001). On multivariate analysis metabolic syndrome was the only independent predictor of ST segment resolution (p=0.01, Odds ratio=2.543, %95 CI:1.248-5.179)Conclusion: The patients with metabolic syndrome had lower rates of complete ST segment resolution after thrombolytic therapy for acute myocardial infarction. This finding may contribute to the higher morbidity and mortality of patients with metabolic syndrome.