The intrinsic viscosity, optical anisotropy and spectral properties of DNA molecule gamma-irradiated with the doses of 10, 20 and 30 Gy in water-ethanol solutions with ethanol concentrations 0-6 mol/l are investigated in the work. Specific volume of DNA at all doses used shows a complex non-monotone dependence on the ethanol content with a peculiarity at the alcohol concentration corresponding to the destruction of water structure in the mixed solvent (so-called, critical concentration, 3.5 mol/l). Ethanol presence at the concentrations below the critical one protects macromolecule from the radiation action. At the alcohol concentrations larger the critical an inversion of the dose dependence of the DNA specific volume is observed. At that the equilibrium rigidity and secondary structure of macromolecule do not change noticeably. The results obtained indicate a significant role of the solvent structure in radiation damage of DNA molecule.