To further improve heat insulation and mechanical properties, silica aerogels were impregnated into highly porous yttria-stabilized zirconia (YSZ) ceramics with well-distributed pores fabricated by tert-butyl alcohol -based gel-casting process and pressureless sintering. Pore size distribution, room-temperature thermal conductivities, and compressive strength of the YSZ ceramics before and after impregnation with silica aerogels were examined and compared, respectively. After impregnating porous YSZ ceramics with silica aerogels, the porosity displayed a little decrease, whereas the pore size significantly decreased by one order of magnitude. Based on this microstructure development, the room-temperature thermal conductivities were significantly lowered and the compressive strength was also promoted. Therefore, the heat insulation and mechanical properties could be simultaneously improved by impregnating porous ceramics with silica aerogels.