Microgreen is a class of emerging fresh produce that are generally rich in vitamins, carotenoids, and other phytochemicals. However, their genetic diversity in phytonutrients has yet to be discovered. In this study, 30 varieties of microgreens in the Brassicaceae family were assayed for phytochemical concentrations and antioxidant capacity. Distinct genotypic variations were observed for ascorbic acid, α-tocopherol, phylloquinone, β-carotene, lutein/zeaxanthin, total glucosinolates, total phenolics as well as 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Results indicated that the Brassicaceae microgreens are good sources of antioxidant phytochemicals, although there are substantial variations within and between species. The nutrient data of Brassicaceae microgreens presented in this study provide valuable information to dieticians, nutrition policy makers, and health-conscious consumers, and growers in the selection of nutrient-dense vegetables.