Dislocations, one-dimensional lattice imperfections, are common to technologically important materials such as III-V semiconductors 1 , and adversely affect heat dissipation in e.g., nitride-based high-power electronic devices 2 . For decades, conventional models 3-5 based on nonlinear elasticity theory have predicted this thermal resistance is only appreciable when heat flux is perpendicular to the dislocations. However, this dislocation-induced anisotropic thermal transport has yet to be seen experimentally 6-9 . In this study, we measure strong thermal transport anisotropy governed by highly oriented threading dislocation arrays along the cross-plane direction in micron-thick, single-crystal indium nitride (InN) films. We find that the cross-plane thermal conductivity is more than tenfold higher than the in-plane thermal conductivity at 80 K when the dislocation density is on the order of ~3×10 10 cm -2 . This large anisotropy is not predicted by the conventional models 3,4 . With enhanced understanding of dislocation-phonon interactions, our results open new regimes for tailoring anisotropic thermal transport with line defects, and will facilitate novel methods for directed heat dissipation in thermal management of diverse device applications.Over the past decade, accurate experiments 10,11 and novel theoretical methods 12-16 have significantly advanced knowledge of lattice imperfections (point defects, dislocations, grain boundaries, etc.) and how these impede thermal transport in crystals and nanostructures. This in-depth understanding has facilitated better thermal management of electronic and optoelectronic devices 17 , design of novel thermoelectric materials 18 and development of sophisticated technologies such as heat assisted magnetic recording 19 and phononic devices 20 . Unlike other defects, the role of dislocations in thermal resistance is still poorly understood. From the theoretical perspective, predictive first-principles calculations 12,13,16 of phonon scattering by dislocations is still nascent, partly due to the large supercells required for their description.Thus, most of the recent theoretical efforts still rely on conventional nonlinear elasticity models 3-5,8 , pioneered by Klemens in the mid-1950s, to describe dislocation-phonon interactions.According to these conventional theories, phonons are elastically scattered by dislocations via two distinct mechanisms: static scattering 3-5 and dynamic scattering 8,21 . Dynamic scattering occurs when mobile dislocations resonantly absorb an incident phonon, vibrate and re-emit a phonon through the process. To have resonant phonon-dislocation interactions, the phonon wavelengths must be comparable to the distance between two pinning points in the dislocations 7 . Phonons with such characteristically long wavelengths are important for heat conduction only at low temperatures (e.g., <10 K), and thus dynamic scattering is insignificant for heat transport at elevated temperatures 8 . Static scattering, on the other hand, can arise from the cores of ...