Background: Obesity is a well-established risk factor for many chronic disorders. However, the effect of weight change after myocardial infarction is well not known. Methods: In whom underwent percutaneous coronary intervention (PCI) consecutively between November 2005 and November 2007 due to acute myocardial infarction (AMI), overweight (23.0���BMI<27.5 kg/���, n=341) and obese (BMI���27.5 kg/���, n=80) patients were selected for analysis. According to weight change, we divided into 4 groups: Group I (weight loss>5%, n=61), Group II (0%<weight loss���5%, n=133), Group III (0%���weight gain<5%, n=181), and Group IV (weight gain���5%, n=46). We assessed association between weight change and major cardiac adverse events (MACE). Results: The higher weight loss, the higher body mass index (Group I: 26.4짹2.8, II: 26.0짹2.6, III: 25.7짹2.0, IV: 25.2짹2.2, p=0.031) and the more diabetes rate (Group I: 34.4%, II: 27.1%, III: 21.2%, IV: 15.2%, p=0.009). However, there were no significant differences in other baseline characteristics including hypertension, dyslipidemia, smoking, gender, and age among groups. Furthermore, there were no significant differences in angiographic and procedural factors including lesion characteristics, procedural success, target vessel, used stent number, and stent size. The higher weight loss, the more MACE rate in 12 months (Group I: 35.8%, II: 23.0%, III: 22.2%, IV: 17.5%, p=0.046). In multivarate analysis, weight loss was a independent predictor for MACE (RR 1.33, 95% CI 1.05-1.67, p=0.017) and mortality (RR 1.80, 95% CI 1.02-3.20, p=0.44) at 12 months. Conclusions: Weight loss after MI is associated with worse outcomes including MACE and mortality at 12 months. Further prospective study is needed to elucidate the effect of weight reduction with intention after MI.