The structure derived potential properties of Graphite such as high stiffness coupled with high thermal conductivity and low coefficient of thermal expansion have been better achieved in Carbon fibers and Carbon-Carbon composites. Consequently, the application domain of carbon-graphite based materials has increased to thermostructural components. These composites are prepared with wide range of reinforcing fibers, high strength carbon fibers to high modulus prepared from PAN, Pitch as well as CVD carbon fibers and carbonaceous material with different compositions as matrix precursor. Both fibers and matrix influence the structure and ultimate properties of carbon/carbon composites. As far as mechanical properties of carbon/carbon composites are concerned the reinforcing carbon fibers are the major load bearing component in carbon-carbon composites. However, the load distribution amongst the fibers through matrix system, the ultimate fracture behaviour and mechanical properties of the composites require judicial control of fiber/matrix interface. Similarly the transport properties like thermal and electrical conductivity depend more on structure and properties of fibers, more so in the direction of the fiber whereas the matrix controls transport properties in the direction perpendicular to reinforcement. The present investigations were undertaken to study thermal properties of the composites and to enhance thermal conductivity of the composites in the direction perpendicular to the fibers through control of matrix microstructure and to study influence of nanocarbon reinforcement addition to the carbonaceous precursors on the microstructure of the matrix as well as on the thermal properties of the ultimate composites. The work incorporated in this report elucidates the thermal conductivity of different types of carbon-carbon composites prepared by the Investigators using different types of carbon fibers and matrix systems.