The thermal diffusivity (a), specific heat (Cp), and thermal conductivity (K) of single phase (Ca1-x,MgxZr4 (PO4)6 (CMZP) ceramic with x=0.4 were investigated in terms of porosity and temperature. The dense CMZP ceramic exhibited values of thermal conductivity lower by a factor of approximately two up to 600°C. The conductivity can be further reduced, to as low as 0.4 W M-1 K-1, by 30% porosity. The temperature dependence of thermal diffusivity became less pronounced with increasing porosity, and a near-constant coefficient of thermal conductivity about 1.1 × 10-4 conduction unit per degree Celsius at temperatures of 30-600 °C, was observed for different porosities. These findings indicate that the CMZP ceramic may be an attractive candidate for thermal insulating applications.