ZrO2 ceramics usually have nonuniform microstructures due to the agglomeration of fine ZrO2 powders. In this paper, the thermal conductivity of porous ZrO2 ceramics with different microstructures was investigated by the laser-flash method. It was found that the thermal conductivity of porous ZrO2 ceramics with uniform microstructure was clearly lower than that of ceramics with nonuniform microstructure. Scanning electron microscopy observations showed that porous ceramics with nonuniform microstructures have wider pore and grain size distributions, relative to those with uniform microstructures. Theoretical analyses were done to model the thermal conductivity of porous ceramics using an effective medium approach. These analyses revealed that matrix grain size distribution has a significant impact on the thermal conductivity of porous ceramics, while the effect of pore size istribution is negligible.