Using apolipoprotein E knock-out (apoE<sup>-/-</sup>) mice on a high fat (HF) diet as an atherosclerotic obesity model, we demonstrated 1) microRNA-155 (miRNA-155, miR-155) is significantly up-regulated in the aortas of apoE<sup>-/-</sup> mice, and miR-155 deficiency in apoE<sup>-/-</sup> mice inhibits atherosclerosis; 2) apoE<sup>-/-</sup>/miR-155<sup>-/-</sup> (double knock-out (DKO)) mice show HF diet-induced obesity, adipocyte hypertrophy, and present with non-alcoholic fatty liver disease; 3) DKO mice demonstrate HF diet-induced elevations of plasma leptin, resistin, fed-state and fasting insulin and increased expression of adipogenic transcription factors but lack glucose intolerance and insulin resistance.