Background: Chronic kidney disease (CKD) significantly and independently affects outcome in patients with acute myocardial infarction (AMI). The level of hematocrit and hemoglobin is a strong prognostic marker in CKD patients with AMI. We investigated whether hematocrit could predict in-stent restenosis (ISR) in CKD patients with AMI who underwent percutaneous coronary intervention (PCI). Methods: Between Nov 2005 and Dec 2006, 80 AMI patients (72짹7 years of age; 70% male) with CKD underwent PCI and follow-up coronary angiography (CAG) at 6-month. CKD was defined by the estimated glomerular filtration rate < 60 ml/min per 1.73 m². The patients were categorized according to the presence of ISR in follow-up CAG. Results: Initial diagnosis were ST-elevation myocardial infarction in 52 (65%), non-ST elevation myocardial infarction in 28 (35%). Baseline characteristics (age, sex, body mass index, risk factors, left ventricular ejection fraction in echocardiogram) between the group with ISR (n= 23) and without ISR (n = 57) were not significantly different. The rate of drug-eluting stents was not significantly different between the group with ISR (67.7 %) and without ISR (77.8 %). The level of hematocrit was lower in patients with ISR than in those without ISR (37.0짹5.7 vs 30.6짹5.1, p=0.001). At the standard cutoff of < 37 %, the lower level of hematocrit indicated a high probability of ISR (odds ratio 1.59, 95% confidence interval 1.1 to 2.2, p=0.041). In multivariate analysis, the level of hematocrit level was an independent predictor for ISR (odds ratio 1.23, 95% confidence interval 1.1 to 1.4, p=0.003). Conclusion: The level of hematocrit could be a predictor of ISR in CKD patients with AMI.