Isothiocyanates and indoles (e.g. indole-3-carbinol) from Brassica vegetables (e.g. broccoli) induce Phase I and Phase II enzymes responsible for the oxidation, reduction and metabolism of endogenous and exogenous carcinogens. Brassica vegetables also contain micronutrients that may provide additional DNA protection from reactive oxygen species. This randomized crossover trial (n = 20) compares the effects of a Brassica Vegetable (BV) intervention against a Micronutrient and Fiber Supplementation (M+F) intervention on urinary F2-isoprostane levels (F2-iP), a stable biomarker of systemic oxidative stress. Brassica intake was monitored by repeated 24 h recalls, urinary ITC levels and questionnaire. Urinary F2-iP levels were measured by mass spectrometry from first-morning urine samples collected at Baseline and after each intervention, and change in natural log transformed urinary F2-iP levels were analyzed using repeated measures regression. Brassica consumption increased from 2 grams/day (g/d) during the Baseline or M+F intervention periods to 218 g/d during the BV intervention, whereas exposure to most antioxidant vitamins and minerals was greatest during the M+F intervention. F2-iP levels significantly decreased by 22.0 or 21.8% during the BV intervention compared with Baseline or the M+F intervention (P = 0.05, P = 0.05, respectively). Urinary F2-iP levels did not significantly differ between Baseline and the M+F intervention (difference = 0.2%; P = 0.98). Brassica intake has been associated with reduced risk of colon, lung, bladder, breast, prostate and other cancers. Our results suggest that Brassica consumption reduces systemic oxidative stress independent of the vitamin and mineral content of these vegetables.