Carbon nanotube (CNT) nanocomposites with a polystyrene thermoplastic matrix were injection molded and the high shear stress exerted during the injection process partially enabled the alignment of the CNTs in the flow direction. Nanocomposites with different CNT loadings and degrees of alignment were produced, and their thermal conductivities were measured based on ASTM D5470. The results were compared with compression molded samples featuring random alignments of CNTs. The results showed that the injection molded samples possessed anisotropic thermal conductivities, due to the partial alignment of the CNTs in the flow direction. The effective medium approach was used to analytically estimate the thermal conductivity of the molded samples. Good agreement was observed between the experimental and analytically simulated results in lower CNT concentrations (less than 5 wt% of CNT). Using transmission electron microscopy pictures taken of the nanocomposites, the alignment of CNTs in the thermoplastic matrix were modeled; and their thermal conductivities were simulated using the finite element method. Good agreement was observed between the experiments and simulated results. POLYM. ENG. SCI., 55:753-762, 2015. (c) 2014 Society of Plastics Engineers