AbstractBetalains, which consist of the subgroups betaxanthins and betacyanins, are hydrophilic pigments that have classically been used for food colorants. Owing to their strong antioxidant property, their usefulness for application for therapeutic use is also expected. In addition, as betalains are mainly naturally available from plants of the order Caryophyllales, including beet (Beta vulgaris), metabolic engineering for betalain production in crops such as vegetables, fruits and cereals may provide new food resources useful for healthcare. Here we conducted metabolic engineering of betacyanins in tomato fruits and potato tubers. The transgenic tomato fruits and potato tubers with coexpression of betacyanin biosynthesis genes, CYP76AD1 from B. vulgaris, DOD (DOPA 4,5‐dioxygenase) and 5GT (cyclo‐DOPA 5‐O‐glucosyltransferase) from Mirabilis jalapa, under control of suitable specific promoters, possessed dark red tissues with enriched accumulation of betacyanins (betanin and isobetanin). The anti‐inflammatory activity of transgenic tomato fruit extract was superior to that of wild‐type fruit extract on macrophage RAW264.7 cells stimulated with lipopolysaccharide (LPS), as a result of decreased LPS‐stimulated transcript levels of proinflammatory genes. These findings were in accord with the observation that administration of the transgenic tomato fruits ameliorated dextran sulfate sodium (DSS)‐induced colitis as well as body weight loss and disease activity index in mice, via suppression of DSS‐stimulated transcript levels of pro‐inflammatory genes, including Tnf (encoding TNF‐alpha), Il6, and Ptgs2 (encoding cyclooxygenae 2). Intriguingly, given the fact that the transgenic potato tuber extract failed to enrich the anti‐inflammatory activity of macrophage cells, it is likely that metabolic engineering of betacyanins will be a powerful way of increasing the anti‐inflammatory property of ordinary foods such as tomato.