In this study, we examined the effect of CLA isomers in preventing age-associated muscle loss and the mechanisms underlying this effect, using 12-months-old C57BL/6 mice fed 10% corn oil (CO) or a diet supplemented with 0.5% c9t11-CLA, t10c12-CLA, or c9t11-CLA+t10c12-CLA (CLA-mix) for 6 months. Both t10c12-CLA and CLA-mix groups showed significantly higher muscle mass, as compared to CO and c9t11-CLA groups, measured by dual-energy X-ray absorptiometry and muscle wet weight. Enhanced mitochondrial ATP production, with higher membrane potential, and elevated muscle antioxidant enzymes (catalase and glutathione peroxidase) production, accompanied by slight increase in H2O2 production was noted in t10c12-CLA and CLA-mix groups, as compared to that of CO and c9t11-CLA groups. Oxidative stress, as measured by serum malondialdehyde and inflammation, as measured by LPS-treated splenocyte IL-6 and TNF-α, were significantly less in CLA isomers groups. Thus, CLA may be a novel dietary supplement that will prevent sarcopenia by maintaining redox balance during aging. © 2009 Elsevier Inc. All rights reserved.