<jats:sec> <jats:title>Objective—</jats:title> <jats:p>Despite advances in stent technology for vascular interventions, in-stent restenosis (ISR) because of myointimal hyperplasia remains a major complication.</jats:p> </jats:sec> <jats:sec> <jats:title>Approach and Results—</jats:title> <jats:p>We investigated the regulatory role of microRNAs in myointimal hyperplasia/ISR, using a humanized animal model in which balloon-injured human internal mammary arteries with or without stenting were transplanted into Rowett nude rats, followed by microRNA profiling. miR-21 was the only significantly upregulated candidate. In addition, miR-21 expression was increased in human tissue samples from patients with ISR compared with coronary artery disease specimen. We systemically repressed miR-21 via intravenous fluorescein-tagged-locked nucleic acid-anti-miR-21 (anti-21) in our humanized myointimal hyperplasia model. As expected, suppression of vascular miR-21 correlated dose dependently with reduced luminal obliteration. Furthermore, anti-21 did not impede reendothelialization. However, systemic anti-miR-21 had substantial off-target effects, lowering miR-21 expression in liver, heart, lung, and kidney with concomitant increase in serum creatinine levels. We therefore assessed the feasibility of local miR-21 suppression using anti-21–coated stents. Compared with bare-metal stents, anti-21–coated stents effectively reduced ISR, whereas no significant off-target effects could be observed.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion—</jats:title> <jats:p>This study demonstrates the efficacy of an anti-miR–coated stent for the reduction of ISR.</jats:p> </jats:sec>