Thermal conductivity (TC) of injection-molded main-chain smectic liquid-crystalline polymers and the composites containing hexagonal boron nitride (h-BN) particles is investigated. Shear flow during injection molding induces alignment of chain-folding lamellar crystals of polymer matrices, in which polymer chains are aligned in the normal direction (ND) with respect to the molding surface, thus leading to a high TC (1.2 W m−1 K−1) in the ND. The composites exhibit a dramatic enhancement of TC in not only the ND but also the in-plane direction. The enhanced TC is much higher than that of common thermoplastic composites at comparable loading levels. These results indicate that the polymer matrices serve as effective heat conductors between h-BN particles.