This paper proposes an approach to the determination of the thermal conductivity coefficient of the inhomogeneous multiphase material when thermal properties of the individual phases are known. This approach is very similar to the method of determining the effective stress-strain properties. Problems in determining the effective thermal characteristics are analyzed based on the temperature distribution over the computational domain and solving problems of heat conduction. This work offers the method of calculating the thermal conductivity coefficient of the inhomogeneous material by solving steady and transient heat conduction problems.