Thermal conductivity of boron nitride is extremely anisotropic. To solve this problem, aggregate boron nitride (A-BN) was fabricated using binder. However, it is easily broken by external forces and has poor wettability. In this study, a new substance that overcomes these issues was introduced. Its coating material was prepared through a hydrolysis and condensation reaction involving polysilazane (PSZ) and (3-glycidyloxypropyl)tri-methoxysilane (GPTMS); The PSZ protected the shape of the A-BN and the GPTMS enhances its wettability. After solving these inherent problems of A-BN, the thermal conductivity was 7.014 W/m*K at a filler fraction of 50 vol %, which was 50 times higher than that of a neat epoxy composite.