Nafion-117 membranes in the Na+-forms with pore-intercalated mixtures of aprotic organic solvents have been obtained. Dependences of solvent uptake of the membranes versus their pretreatment conditions and compositions of initial organic solvent mixtures are described. Ionic conductivity of the obtained membranes in the temperature range -20-50 degrees C is investigated using impedance spectroscopy. It is demonstrated that ionic conductivity increases with increasing solvent uptake. The highest conductivities at 30 degrees C (similar to 4 mS/cm) are obtained for the membranes thermally treated in methanol and aged in ethylene carbonate-dimethylacetamide, ethylene carbonate-diethyl carbonate-dimethylacetamide and propylene carbonate-dimethylacetamide-tetrahydrofuran mixtures. Thermal stability is studied by differential scanning calorimetry. It is shown that the membrane with intercalated propylene carbonate-dimethylacetamide-tetrahydrofuran mixture is characterized by a constant phase composition in a broad temperature range (up to -100 degrees C) and retention of high conductivity at low temperatures (similar to 1 mS/cm at - 20 degrees C).