MicroRNAs (miRNAs) are noncoding RNAs that impact almost every aspect of biology and disease. Until now, the cell-specific effects of miRNAs in cardiovascular system have not been established. In the current study, the cellular functions of miR-221 and miR-222 (miR-221/222) in vascular smooth muscle cells (VSMCs) and vascular endothelial cells (ECs) were compared. In cultured cells, we identified that the effects of miR-221/222 on proliferation, migration, and apoptosis are opposite between VSMCs and ECs. In VSMCs, miR-221/222 had effects of pro-proliferation, pro-migration, and anti-apoptosis. In contrast, miR-221/222 had effects of anti-proliferation, anti-migration, and pro-apoptosis in ECs. The different expression profiles of their target genes, p27(Kip1), p57(kip2), and c-kit between the two cell types might be related to the opposite effects. Finally, the opposite cellular effects of miR-221/222 were verified in vivo in balloon-injured rat carotid artery as demonstrated by different consequences in neointimal growth and re-endothelialization. The results suggest that the biological functions of miR-221/222 in vascular walls are cell-specific. The opposite cellular effects of miR-221/222 on VSMCs and ECs may have important therapeutic applications in many vascular diseases such as atherosclerosis and restenosis after angioplasty.