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Antioxidant activity of betalain pigments (seven pure compounds and four combined fractions) from plants of the family Amaranthaceae was evaluated using the modified DPPH^• (1,1-diphenyl-2-picrylhydrazyl) method. All tested betalains exhibited strong antioxidant activity. Their EC₅₀ values ranged from 3.4 to 8.4 μM. Gomphrenin type betacyanins (mean = 3.7 μM) and betaxanthins (mean = 4.2 μM) demonstrated the strongest antioxidant activity, 3−4-fold stronger than ascorbic acid (13.9 μM) and also stronger than rutin (6.1 μM) and catechin (7.2 μM). Antioxidant activity of the tested betalains decreased in the following order:  simple gomphrenins > acylated gomphrenins > dopamine-betaxanthin > (S)-tryptophan-betaxanthin > 3-methoxytyramine-betaxanthin > betanin/isobetanin > celosianins > iresinins > amaranthine/isoamaranthine. This study also investigated and discussed the relationship between the …