In the study the ability of dihydroquercetin to inhibit the development of free radical reactions in the process of storing a new animal extracted product «Splenaktiv» (SA), which is a freeze-dried aqueous extract of the cattle spleen, was investigated. SA was prepared without (SA-1) and with dihydroquercetin supplement as an antioxidant (SA-2). The antioxidant activity of SA-1 and SA-2 and the content of lipid peroxidation product — malondialdehyde — were determined before and after storage for 2 years. It was found that after the period of storage of the selected antioxidant activity of the animal extracted product SA-1 decreased by10 times, and the content of malondialdehyde increased by 2 times as compared to baseline (p <0.01), whereas in the case of SA-2 the appropriate parameters practically did not change. Thus, the use of dihydroquercetin as an antioxidant in the composition of SA inhibits the development of oxidation processes and increases its shelf-life.