The objective of the research study was to assess the antioxidant activity of beers produced using unmalted quinoa (seeds or flakes) or amaranth (seeds, flakes, or popped seeds) as substitutes for 10 and 30 % of malt from barley. The antioxidant activity of the beers studied was determined based on the effectiveness of quenching a synthetic DPPH˙⁺ radical and the ability to reduce ferric ion by a FRAP method. Under the research studies conducted, the content of polyphenols was also determined by a spectrophotometric method. The reducing ability of beers produced with added 10 % of unmalted amaranth seeds or flakes was higher compared to the beers manufactured solely from barley malt. Compared to the beers manufactured wholly from malt, the antiradical activity of beers did not decreased where any form of quinea was used to substitute the amount of 10 % of malt. The application of unmalted polyphenols-rich pseudocereals as a substitute for malt did not cause the content of those compounds in the final beer to increase. In the case the amaranth or quinoa seeds substituted 30 % of the barley malt, it was found that the reducing potential of the produced beers significantly decreased compared to beers produced with 10 % of pseudocereals added and to beers produced exclusively from barley malt. The completed research study has not given a clear-cut answer whether or not the quinea or amaranth cause the antioxidant activity of beers produced with them to increase, and, consequently, the shelf life of those beers to become longer. More research on this subject is indispensable including, among other things, the analysis of fatty acids added to beer along with pseudocereals.