||As electronic devices such as mobile phones, labtops, and automobiles are highly integrated and miniaturized, a large amount of heat is generated in the driving time. This heat degrades the performance of device, and causes malfunction and poor durability. So it is important to release the heat to the outside. In this study, polyurethane(PU)/modified boron nitride(m-BN) composites were prepared for heat radiating film. PU has flexibility and excellent tensile strength. In addition, the physical property of PU can be easily controlled through the molecular design. However, PU is unstable in heat and burn easily, so its use is limited in the field where there is a risk of fire. To solve this problem, BN was modified with organo-phosphorus incorporated silane coupling agent. The characterization of PU/m-BN composite was investigated by fourier transform-infrared(FT-IR) spectrometer, differential scanning calorimetry (DSC), thermogravimetric analysis(TGA) and laser flash analysis(LFA).