Abstract:The seeds of Celosia argentea L.(yellow flower) were carried by a high altitude balloon(CHAB) at an altitude of 40.112 km above sea level for about 4 hours. After the balloon returned on the ground, the treated seeds were stored for 8 months at 4℃ and then sowed. The inflorescences and leaves of the first generation were used for water extraction. The effects of water extracts from inflorescences and leaves of treated and control plants on scavenging of superoxide radical (O2-· ) and hydroxyl radical (·OH) were studied by colorimetric method，and the contents of Vitamin C， flavonol and the activity of SOD of all samples were determined． The results showed that the water extracts could reduce ·OH induced oxidation of reductive Cyt·C(II) and inhibit O2-·， induced oxidation of hydroxylamine．The effects of water extracts from treated plants on scavenging active oxygen were more significant than those from the control，indicating that high altitude condition treatment could increase an tioxidation activityin cookscombs.