Background:Aberrant expression of microRNAs is associated with neointimal hyperplasia (NIH) in type 2 diabetes. We prospectively compared the effects of pioglitazone on coronary NIH and changes in microRNAs according to NIH status in type 2 diabetic patients during 9-month follow-up.Methods and Results:Type 2 diabetic patients were randomly assigned to the pioglitazone (n=36) or control groups (n=36) after coronary stenting. Primary endpoint was the comparison of changes in neointimal volume on OCT and in the level of circulating microRNA-17,-24,-92a,-126 and -145 during 9-month follow-up. Secondary endpoint was the comparison of changes in brachial artery flow-mediated dilation and inflammatory markers such as IL-6, TNF-α, hsCRP, adiponectin, sICAM-1, and sVCAM-1 between the 2 groups. Neointimal volume was significantly lower in the pioglitazone group (25.02±17.78 mm³vs. 55.10±30.01 mm³, P<0.001) with significant increases in circulating microRNA-24 (0.264±0.084 vs. 0.006±0.030, P<0.001) during follow-up. FMD was significantly greater in the pioglitazone than control group at 9 months (0.47±0.14 mm vs. 0.28±0.18 mm, P<0.05, respectively). Decreases in inflammatory markers such as IL-6, TNF-α, and sVCAM-1 were significantly greater in the pioglitazone than the control group during the follow-up.Conclusions:Pioglitazone significantly decreased NIH with increases in circulating microRNA-24 at 9-month follow-up. The decrease in microRNA-24 could be used as a potential predictor of increases in NIH in type 2 diabetic patients. (Circ J 2015; 79: 880–888)