Background: Few studies have serially monitored the change of coronary plaque after statin therapy using multiple plaque imaging modalities. Methods and Results: A prospective open-label trial was performed to assess coronary plaque regression and stabilization following 52 weeks of pitavastatin treatment (2 mg/day). Coronary segments that included the most diseased plaque of 90 patients determined on angioscopy were analyzed using intravascular ultrasound (IVUS). The yellow grade of each plaque of 46 patients who had matched angioscopy and IVUS data was evaluated on angioscopy. Low-density lipoprotein-cholesterol (LDL-C) was reduced 34.5% (145.0±24.0 mg/dl to 93.6±22.6 mg/dl, P<0.001), and high-density lipoprotein cholesterol increased 17.8% (44.9±11.1 mg/dl to 51.9±11.7 mg/dl, P<0.001). Yellow grade decreased (2.9±0.8 to 2.6±0.7, P=0.040) during 52 weeks. The reduction of yellow grade was not correlated with the LDL-C level at 52 weeks or its change. The change of yellow grade was inversely correlated with maximum yellow grade at baseline. Percent atheroma volume on IVUS did not change during 52 weeks, but its change for 52 weeks was significantly correlated with LDL-C level at 52 weeks (Spearman's rank correlation coefficient 0.312, P=0.035). Conclusions: Fixed dose pitavastatin stabilized vulnerable coronary plaques by the reduction of yellow grade without significant reduction of plaque volume. The stabilization and regression of atherosclerotic plaques by statin may differ, but both nonetheless contribute to the reduction of cardiovascular events (UMIN Clinical Trials Registry UMIN000001107).  (Circ J 2010; 74: 1922 - 1928)