The development of advanced thermal transport materials is a global challenge. Two-dimensional nanomaterials have been demonstrated as promising candidates for thermal management applications. Here, we report a boron nitride (BN) nanosheet/polymer composite film with excellent flexibility and toughness prepared by vacuum-assisted filtration. The mechanical performance of the composite film is highly flexible and robust. It is noteworthy that the film exhibits highly anisotropic properties, with superior in-plane thermal conductivity of around 200 W m -1 K -1 and extremely low through-plane thermal conductivity of 1.0 W m -1 K -1 , making this material an excellent candidate for thermal management in electronics. Importantly, the composite film shows fire-resistant properties. The newly developed unconventional flexible, tough, and refractory BN films are also promising for heat dissipation in a variety of applications.