The effects of quercetin (1) were investigated on disused muscle atrophy using mice that underwent tail suspension. Periodic injection of 1 into the gastrocnemius muscle suppressed muscle weight loss and ubiquitin ligase expression. Compound 1 reduced the enhancement of lipid peroxidation in the muscle. Injection of N-acetyl-l-cysteine, but not flavone (2), also prevented muscle weight loss and enhancement of lipid peroxidation. These findings demonstrate that 1 can prevent disused muscle atrophy by attenuating the expression of ubiquitin ligases and that such prevention originates from its antioxidant activity.