It has recently received much interest to incorporate a specific gradient function to a composite, according to the specific application of the composite. The composition profiles, as well as the microstructures of such materials have to be optimized with respect to the intended material function. For this reason the compositional dependence of the material properties are needed to obtain an optimum design, usually by means of numerical calculations. In present study, the dependence of the thermal conductivity of sintered Mo/ZrO₂ composite on composition and microstructure were investigated, which is necessary information for the design of a thermal-stress release type functionally graded material. It was found that the thermal conductivity of the sintered Mo/ZrO₂ composite exhibits a S curve against composition. The shape of S curve depends not only on the composition but also on the composite microstructure. The compositional dependence of the thermal conductivity of this composite was discussed in relation to theories that have so far been proposed. A fitting method for the experimental data was proposed on the basis of theoretical equations, in which microstructural transition in these sintered composites was taken into account.