The effects of elevated CO2 concentrations on the antioxidant capacity and flavonoid content in strawberry fruit (Fragaria x ananassa Duch.) were studied under field conditions. Increased CO2 (300 and 600 mol mol-1 above ambient) concentrations resulted in increases in ascorbic acid (AsA), glutathione (GSH), and ratios of AsA to dehydroascorbic acid (DHAsA) and GSH to oxidized glutathione (GSSG), and a decrease in DHAsA in strawberry fruit. High anthocyanin and phenolic content were also found in fruit of CO2 treated plants. Growing strawberry plants under CO2 enrichment conditions significantly enhanced fruit p-coumaroylglucose, dihydroflavonol, quercetin 3-glucoside, quercetin 3-glucuronide, and kaempferol 3-glucoside contents, as well as cyanidin 3-glucoside, pelargonidin 3-glucoside, and pelargonidin 3-glucoside-succinate content. Fruit of strawberry plants grown in the CO2 enrichment conditions also had high oxygen radical absorbance activity against ROO, O2-, H2O2, OH, and 1O2 radicals.