Compost as a soil supplement significantly enhanced levels of ascorbic acid (AsA) and glutathione (GSH) and ratios of AsA/dehydroascorbic acid (DHAsA) and GSH/oxidized glutathione (GSSG) in fruit of two strawberry (Fragaria ¥ ananassa Duch.) cultivars, Allstar and Honeoye. The peroxyl radical (ROO) as well as the superoxide radical (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH), and singlet oxygen (1O2) absorbance capacity in strawberries increased significantly with increasing fertilizer strength and compost use. The planting medium (compost) ¥ fertilizer interaction for phenolics and flavonoids was significant. Fruit from plants grown in full-strength fertilizer with 50% soil plus 50% compost and 100% compost yielded fruit with the highest levels of phenolics, flavonol, and anthocyanin content. A positive relationship between antioxidant activities and contents of AsA and GSH and ratios of AsA/DHAsA and GSH/GSSG existed in fruit of both strawberry cultivars. Correlation coefficients for the content of antioxidant components versus antioxidant activity [against ROO, O2-, H2O2, OH, or 1O2] ranged from r = 0.7706 for H2O2 versus GSH/GSSH in cv. Allstar to r = 0.9832 for O2- versus total flavonoids in cv. Allstar.