We determined time course of stabilization of echolucent carotid plaques by statin therapy in patients with acute coronary syndrome (ACS). Treatment with 4 mg/d pitavastatin (n = 33) or placebo (n = 32) was initiated within 3 days after onset of ACS in 65 patients with echoluceit carotid plaque. Vulnerable carotid plaques were assessed by measuring plaque echolucency using carotid ultrasound with integrated backscatter (IBS) analysis before and 1 month after treatment in all patients. The calibrated IBS value (intima-media IBS value minus adventias IBS) of vulnerable carotid plaques favorably changed at I month after treatment in both groups, but the echolucency at I month improved more in the pitavastatin than in the placebo group (pitavastatin group: -18.7 +/- 3.3 dB at pretreatment versus -12.7 +/- 2.3 dB at I month *P < 0.001; placebo: -19.0 +/- 3.5 dB versus -16.9 +/- 3.2 dB, P < 0.05, *P < 0.01 versus the value at I month in placebo group). Levels of CRP, VEGF, and TNF alpha at I month were significantly lower in pitavastatin than placebo group. In conclusion, pitavastatin improved carotid plaque echolucency within I month of therapy in patients with ACS, in association with decrease in the inflammatory bionnarkers related to vulnerable plaques.