The effective thermal conductivity (ETC) of fluid-saturated porous mica ceramics with open pores was measured over a temperature range from 275 to 423 K and at pressures up to 400 MPa using a steady-state parallel-plate apparatus. It is an absolute, steady-state measurement device with an operational temperature range of 273-1273 K and a pressure range up to 1500 MPa. We used argon and water as pore saturants. The estimated accuracy of the method is +/-2%. The porosity of the samples was 2%, 14%, and 26%. The effect of pressure, temperature, and porosity on the ETC behavior of the fluid (Ar and H2O)-saturated porous mica ceramic was studied. A sharp increase of the ETC was found for porous mica ceramic with gas (Ar) saturated at low pressures (between 0.1 and 100 MPa) along the various isotherms, while for the same sample saturated with water, the pressure dependence of the ETC displayed very weakly. The measured values of the ETC for a fluid-saturated porous mica ceramic were compared with the values predicted by various theoretical and semiempirical models. The effect of the size, shape, and distribution of the pores on the ETC of porous mica ceramic was discussed.