Fish oil (FO) is known to reduce triglyceride synthesis and improve insulin sensitivity in liver which may account for its anti-atherogenic effects. The objective of this study was to investigate the role of white adipose tissue (WAT), another important insulin responsive tissue, in mediating the anti-atherogenic effect of FO. Female LDL receptor-deficient mice were fed a high fat diet enriched with 6% olive oil (control) or 6% menhaden oil (FO) for 12 weeks. FO feeding led a to a significant (47%) reduction in atherosclerotic lesion formation. In addition to improving serum and liver lipid profiles, FO-feeding also led to a significant decrease in cholesteryl ester, phospholipid and free fatty acid levels in WAT. FO-fed animals showed a significant reduction in expression of inflammatory mediators in WAT, which could be attributed to a reduction in activation of mitogen activated protein kinases. Insulin sensitivity in WAT of FO-fed mice was improved, as indicated by increased phosphorylation of the insulin receptor. Finally, we found that FO reduced the formation of F2 isoprostanes in both liver and WAT with a concomitant increase in the formation of the protective EPA and DHA-derived F3 and F4 isoprostanes; providing evidence that FO-feeding also improves oxidative stress. Taken together, these data clearly suggest that in addition to playing a role in hepatic lipid homeostasis, FO could also exert its anti-atherogenic effect by improving WAT function (supported in part by grants from the NIH (P01 ES013125), the American Diabetes Association (1-04-JF-20) and the American Heart Association (0330011N).