A study of the antiviral activity of antioxidants against viral infections is believed to be essential for creating complex antiviral agents. Dihydroquercetin is considered as the most active antioxidant extracted from Larix gmelinii. In this work, we present results of experiments of the antiviral properties of dihydroquercetin against a member of the family Picarnaviridae--Coxsackievirus B4 in vitro. We have estimated that dihydroquercetin reduces viral titers at 100 µg/ml concentration as compared with control of virus. We have shown using the plaque assay that CPE of virusis reduced in the presence of dihydroquercetin at 100 µg/ml. Study of the phase of viral lifecycle, in which dihydroquercetin acted, demonstrated that the highest efficacy of the antiviral therapy was reached at early stages of virus reproduction (1-3 hours post infection). These results show that dihydroquercetin has antiviralproperty against Coxsackievirus B4. This drug and other antioxidants can be tested as inhibitors of viral replication.