Porous yttria-stabilized zirconia (YSZ) ceramics were fabricated using tert-butyl alcohol (TBA)-based gelcasting with monodisperse polymethylmethacrylate (PMMA) microspheres as both pore-forming agent and lubricant agent. The TBA-based slurry of 50 vol% solid loading with excellent rheological properties appropriate for casting was successfully prepared by using a commercial polymer dispersant DISPERBYK-163 as both dispersant and stabilizer. The distribution of the spherical pores made from PMMA microspheres was very homogeneous. Their average diameter decreased from 16.9 to 15.7 μm when the sintering temperature was increased from 1350°C to 1550°C. The compressive strength increased from 14.57 to 142.29 MPa and the thermal conductivity changed from 0.17 to 0.65 W/m·K when the porosity decreased from 71.6% to 45.1%. The results show that this preparation technology can make all the main factors controllable, such as the porosity, the size and shape of pores, the distribution of pores, and the thickness and density of pore walls. This is significant for fabricating porous ceramics with both high compressive strength and low thermal conductivity.