Abstract: Graphitized polyimide films (GPFs) and tapes (GPTs) were coated with epoxy resin (EP), and their EP composites were prepared by hot-pressing the laminated GPFs and stacked GPTs. The crystal structure, morphology and optical texture of the GPFs and GPTs as well as their EP composites were characterized by X-ray diffraction, scanning electron microscopy and polarized light microscopy. The effects of volume fraction and the dimensions of the GPFs and GPTs on the thermal conductivity of their composites were investigated. The thermal conductivity and thermal diffusion coefficient of GPT/EP composites increased with GPT volume fraction. The thermal conductivity in different locations perpendicular to the hot-pressing direction of a GPT/EP composite stacked with 80% GPTs varied between 453 W (m·K)⁻¹ to 615 W (m·K)⁻¹ due to the gap between the GPTs. The GPF/EP composite laminated with 80% GPF has a highly oriented sandwich structure, which has an in-plane thermal conductivity of 894 W (m·K)⁻¹. However, the thermal conductivities of GPT/EP and GPF/EP composites with 80% GPTs or GPFs along the hot-pressing direction were 1.82 and 1.15 W (m·K)⁻¹, respectively. The obvious difference in the thermal conductivities perpendicular and parallel to the hot-pressing direction confirms that the two composites are highly anisotropic.