Boron nitride (BN) is a prospective filler for dielectric applications as due to its high thermal conductivity and excellent electrical insulating ability. However, the inert characteristic of BN makes it difficult to be modified and results in poor dispersion in polymer matrix. In this study, we firstly activated the surface of BN by using strong oxidizing nitric acid. In this way, positively charged silane coupling agent could be easily grafted to BN, then a surface modification of BN with negatively charged graphene oxide (GO) was achieved through electrostatic self-assembly. The successful absorption of GO on the surface of BN (BN@GO) was confirmed by SEM, Raman spectra and EDX. After being incorporated in epoxy matrix and reduced during processing, BN@rGO was found to be effective to not only enhance the thermal conductivity of epoxy composites, but also largely increase the dielectric constant and decrease the dielectric loss which was even lower than that of neat epoxy. The improved dielectric properties of epoxy/ BN@rGO nanocomposites was ascribed to the enhanced interaction between modified BN and epoxy matrix, and synergic effect between BN and rGO. We believe that our work provides a new solution to modify BN and can be used as an effective method to fabricate dielectric materials with both good capability of heat dissipation and dielectric properties.