This trial is consisted of 6 weeks of wash out for the patients already taking statin. After that, daily 4 grams of omega-3 acid(OMACOR) will be administered for 10 weeks. Before and after the administration of study drug, we will measure the change of the amount of plasma small dense LDL via ultracentrifuge/non-denaturing polyacrylamide gel electrophoresis followed by oil red O and coomassie blue staining. As a secondary outcome measure, we will also assess the change of HDL(high density lipoprotein) cholesterol sub-type by the same method.