<p><b>Abstract</b>—Thermal conductivity of carbon fibers used as reinforcements is a very important property that defines effectiveness of composite materials for heat insulation and heatsink applications. Nevertheless, no thermal conductivity data are available for many commercial carbon fibers from either the manufacturers’ datasheets or academic sources; this fact may be linked with measurement problems for yarn- and filament-like specimens. In the present study, we assess the possibility to evaluate the thermal conductivity of carbon fibers with known Young’s moduli on the basis of empirical correlations established for commercial carbon fiber types. Empirical equations correlating Young’s moduli and thermal conductivities of carbon fibers have been established, and calculated and experimental values of thermal conductivities for several domestic polyacrylonitrile-based carbon fibers have been compared. For rayon-based fibers, published data are scarce, so calculated values were compared with expected ranges. Possible explanations of the observed correlations are proposed with consideration of the structure-dependent properties of the materials under study. The proposed equations are intended for use in prediction of thermal conductivity of novel carbon fibers, as well as heat transfer modeling in carbon-fiber reinforced composite materials.</p>