Microgreens are increasingly valued by consumers for their phytonutritional benefits. There is limited information to growers on the influence of growth media and seed density on antioxidant properties of Brassica microgreens. Therefore, the study was conducted to determine the effect of seedling media (Hygromix, Promix, and TS1) and seed density (4, 8, and 12 seeds per seed cavity) on morphological parameters, yield, color, antioxidant components, and their activities in radish (Raphanus sativus), cabbage (Brassica oleracea), and rocket (Eruca sativa) microgreens. Fourteen days after seeding, Promix at a seed density of 12 per cavity improved yield of radish, cabbage, and rocket microgreens. Irrespective of the seed density, all three Brassica microgreens grown in TS1 had higher leaf nitrogen, phosphorus, and calcium content. Interaction effects of Hygromix x seed densities were more pronounced on the antioxidant properties (DPPH and FRAP). These differences could be due to the physical properties of growth medium. Vitamin C and total glucosinolate were improved on Brassica microgreens grown in Hygromix at a seed density of 4 per cavity. Twelve seeds per cavity in Promix growth medium improved Brassica microgreens yield, whereas phytochemicals were most likely improved by growing media, Hygromix followed by TS1 and mineral content improved in TS1 followed by Hygromix at low seed density of 4 per cavity.