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.