Hexagonal boron nitride (h-BN) has a similar layered structure with good thermal conductivity to graphite, but conversely electrically insulating. So h-BN is popular in preparing thermally conducting but electrically insulating materials for dieattachments, encapsulations, dielectrics and substrates used in electronic packaging. However h-BN has generally poor compatibility with most polymer matrix, resulting in weak interaction between surfaces of h-BN and matrix. Interface associated with the surface chemistry of fillers is a critical factor in affecting the properties of filled polymers, including both thermal conductivity and mechanical properties. In this study, we prepared functionalized h-BNencapsulated by graphene oxide through electrostatic self-assembly and added this modified filler into epoxy resin. Fourier-transforminfrared (FT-IR),scanning electron microscope (SEM),Raman spectroscopy and Energy Dispersive X-Ray Spectroscopy (EDX) are characterized to highly prove the encapsulation of graphene oxide. Owing to the rich oxygen-containing functional groups of graphene oxide on the surface of the h-BN, both the thermal conductivity and mechanical properties show obvious enhancement.Meanwhile, the thermal conductivity of polystyrenefilled by h-BN @ reduced graphene oxide (rGO) also largely increased. Moreover, the content of encapsulated graphene oxide or graphene was extremely little (less than 0.2 wt %), so good electrically insulation and low dielectric loss was maintained.