Objective To investigate the relationship between eosinophil and in-stent restenosis in acute coronary syndrome patients. Methods One hundred and fifity-one ACS cases werenenrolled in this study. According to the results of coronary angiography (the stented segment lumen loss over 50% was judged to be ISR), patients were divided into the restenosis group and the non-restenosis group. Results Based on the logistic analysis, no significant association was found between eosinophil and ISR, and even after adjustment of related risk factors (P > 0.05). The stratification analysis showed that the high level of eosinophil might increase the risk of ISR in ACS patients with history of hypertension (P = 0.038) and myocardial infarction (P = 0.032). Conclusion Eosinophil may be associated with the risk of ISR in ACS patients with history of hypertension and myocardial infarction. The underlying mechanisms need to be elucidated in further study.