Background: The apolipoprotein B/A1 (apoB/A1) ratio is a stronger predictor of future cardiovascular disease than is the level ofconventional lipids. Statin and ezetimibe combination therapy have shown additional cardioprotective effects over statin monotherapy. Methods: This was a single-center, randomized, open-label, active-controlled study in Korea. A total of 36 patients with type 2 diabetesmellitus were randomized to either rosuvastatin monotherapy (20 mg/day, n=20) or rosuvastatin/ezetimibe (5 mg/10 mg/day, n=16) combination therapy for 6 weeks. Results: After the 6-week treatment, low density lipoprotein cholesterol (LDL-C) and apoB reduction were comparable betweenthe two groups (–94.3±15.4 and –62.0±20.9 mg/dL in the rosuvastatin group, –89.9±22.7 and –66.8±21.6 mg/dL in the rosuvastatin/ezetimibe group, P=0.54 and P=0.86, respectively). In addition, change in apoB/A1 ratio (–0.44±0.16 in the rosuvastatingroup and –0.47±0.25 in the rosuvastatin/ezetimibe group, P=0.58) did not differ between the two groups. On the other hand,triglyceride and free fatty acid (FFA) reductions were greater in the rosuvastatin/ezetimibe group than in the rosuvastatin group(–10.5 mg/dL [interquartile range (IQR), –37.5 to 29.5] and 0.0 μEq/L [IQR, –136.8 to 146.0] in the rosuvastatin group, –49.5 mg/dL[IQR, –108.5 to –27.5] and –170.5 μEq/L [IQR, –353.0 to 0.8] in the rosuvastatin/ezetimibe group, P=0.010 and P=0.049, respectively). Both treatments were generally well tolerated, and there were no differences in muscle or liver enzyme elevation. Conclusion: A 6-week combination therapy of low-dose rosuvastatin and ezetimibe showed LDL-C, apoB, and apoB/A1 ratio reductioncomparable to that of high-dose rosuvastatin monotherapy in patients with type 2 diabetes mellitus. Triglyceride and FFAreductions were greater with the combination therapy than with rosuvastatin monotherapy.