Polysaccharide fractions from the mycelium of the lion's mane medicinal mushroom <i>Hericium erinaceus </i>BP 16, cultivated on sterile grain substrates (barley, oats, wheat, rice, rye), were isolated and characterized. One percent solutions were prepared from the resulting fractions, mixed with blood, which was then subjected to cold stress at a temperature of 6°C for 3, 5 and 7 d. It has been shown that the fraction of <i>H. erinaceus </i>grown on rye is characterized by a high content of the protein fraction and arabinose monosaccharide and contributes to the preservation of higher phagocytic, bactericidal and antioxidant activity cells throughout the entire period of stress. Polysaccharide fractions of the fungus <i>H. erinaceus</i>, grown on various grain substrates, can serve as an immunomodulatory and antioxidant food additive and provide significant benefits in the daily life of people with stress and reduced immunity.