The paper presents research results of permeability of hydrogen isotopes through CrNi35WTiAl alloy containing radiogenic helium, and results of hydrogen and radiogenic helium impact on mechanical properties of this alloy. The impact of hydrogen and radiogenic helium on mechanical properties of CrNi35WTiAl alloy was determined by tensile tests of cylindrical samples in inert and hydrogen atmospheres. For this research samples with various concentrations of 3He (90, 230 and 560 appm) were prepared. The buildup of 3He has been fulfilled using the “tritium trick” technique. Maximal influencing of hydrogen and radiogenic helium on mechanical properties of CrNi35WTiAl was observed at 873 K on samples with 560 appm of 3He. Testing of permeability of hydrogen isotopes was made in temperature range from 723 to 973 K.