Improving mitochondrial oxidant scavenging may be a viable strategy for the treatment of insulin resistance and diabetes. Mice overexpressing the mitochondrial matrix isoform of superoxide dismutase (sod2tg mice) and/or transgenically expressing catalase within the mitochondrial matrix (mcattg mice) have increased scavenging of O2.ˉ and H2O2, respectively. Furthermore, muscle insulin action is partially preserved in high fat (HF)-fed mcattgmice. The goal of the current study was to test the hypothesis that increased O2.ˉ scavenging alone or in combination with increased H2O2 scavenging (mtAO mice) enhances in vivo muscle insulin action in the HF-fed mouse. Insulin action was examined in conscious, unrestrained and unstressed wild type (WT), sod2tg , mcattg and mtAO mice using hyperinsuline-mic-euglycemic clamps (insulin clamps) combined with radioactive glucose tracersfollowing sixteen weeks of normal chow or HF (60% calories from fat) feeding. Glucose infusion rates, whole body glucose disappearance, and muscle glucose uptake during the insulin clamp were similar in chow- and HF-fed WT and sod2tg mice. Consistent with ourprevious work, HF-fed mcattg mice had improved muscle insulin action, however, an additive effect was not seen in mtAO mice. Insulin-stimulated Akt phosphorylation in musclefrom clamped mice was consistent with glucose flux measurements. These results demonstrate that increased O2.ˉ scavenging does not improve muscle insulin action in the HF-fedmouse alone or when coupled to increased H2O2 scavenging.