The gene expression and enzyme activity of superoxide dismutase, catalase, and ascorbate peroxidase in the space-grown barley were not significantly different from those of the ground-grown barley. Cu2+ reducing and radical scavenging activities in an extract of the space-grown barley were lower than those of the ground-grown barley by 0.7 fold, suggesting that the space environment does not induce oxidative stress, and reduces antioxidant capacity in plants.