This study was aimed at determination of antioxidant capacity of commercial kvasses. Four different beverages (“Obolon”, “Wileński”, “Gubernija”, and Eko-Natura”) were purchased in local shops in Poland, one beverage (“Brottrunk Biovegan”) originated from the German market. Antioxidan capacity of the beverages was investigated using ABTS, FRAP, and DPPH assays. The content of total phenolic compounds was determined using a Folin-Ciocalteu’s phenol reagent. The profile of phenolic compounds were determined using an HPLC method. The content of total phenolics ranged from 0.083 to 0.372 mg/ml; the TEAC values from 0.133 to 1.001 μmol Trolox/ml; the FRAP values from 0.893 to 3.079 μmol Fe2+/ml. The antiradical activity against DPPH radical ranged from 0.097 to 0.463 μmol Trolox/ml. A strong correlation was noted between the contents of total phenolics and results of antioxidant assays. The presence of benzoic acid in one beverage was confirmed using the HPLC method.