BACKGROUND AND OBJECTIVES: Statins remain the mainstay of secondary coronary artery disease (CAD) prevention, but n-3 polyunsaturated fatty acids (ω-3 PUFA) display biological effects that may also reduce the risk of atherosclerosis and CAD. However, data on the possible antiatherosclerotic benefits of adding ω-3 PUFA to statin therapy are limited. This study aimed to investigate the potential additive effects of ω-3 PUFA on regression of atherosclerosis in CAD patients receiving statin therapy and stent implantation. SUBJECTS AND METHODS: Seventy-four CAD patients undergoing percutaneous coronary intervention (PCI) with stent implantation were enrolled, prescribed statins, and randomly assigned to two groups: n-3 group (ω-3 PUFA 3 g/day, n=38) or placebo group (placebo, n=36). All patients completed the study follow-up consisting of an intravascular ultrasound at baseline and at 12 months. RESULTS: There was no difference in the baseline characteristics and distribution of other medications. No significant differences were observed in primary endpoints, including changes in atheroma volume index (-12.65% vs. -8.51%, p=0.768) and percent atheroma volume (-4.36% vs. -9.98%, p=0.526), and in secondary endpoints including a change in neointimal volume index (7.84 vs. 4.94 mm3/mm, p=0.087). CONCLUSION: ω-3 PUFA had no definite additional effect on the regression of coronary atherosclerosis when added to statin in CAD patients undergoing PCI.