Studying the effects of dietary fish oil on VLDL metabolism in humans is subject to both large intra- and interindividual variability. In the present study we therefore used hyperlipidemic apolipoprotein (APO) E*3-Leiden mice, which have impaired chylomicron and very low density lipoprotein (VLDL) remnant metabolism, to study the effects of dietary fish oil on serum lipids and VLDL kinetics under highly standardized conditions. For this, female APOE*3-Leiden mice were fed a fat- and cholesterol-containing diet supplemented with either 0, 3 or 6% w/w (i.e. 0, 6, or 12% of total energy) of fish oil. Fish oil-fed mice showed a significant dose-dependent decrease in serum cholesterol (up to -43%) and triglyceride levels (up to -60%), mainly due to a reduction of VLDL (-80%). LDL and HDL cholesterol levels were not affected by fish oil feeding. VLDL-apoB kinetic studies showed that fish oil feeding resulted in a significant 2-fold increase in VLDL-apoB fractional catabolic rate (FCR). Hepatic VLDL-apoB production was, however, not affected by fish oil feeding. VLDL-triglyceride turnover studies revealed that fish oil significantly decreased hepatic VLDL-triglyceride production rate (-60%). A significant increase in VLDL-triglyceride FCR was observed (+70%), which was not related to increased lipolytic activity. We conclude that APOE*3-Leiden mice are highly responsive to dietary fish oil. The observed strong reduction in serum very low density lipoprotein (VLDL) is primarily due to an effect of fish oil to decrease hepatic VLDL triglyceride production rate and to increase VLDL-apoB fractional catabolic rate.