To improve the thermal conductivity of h-BN-filled epoxy composite, silane treatment was used to 3-Aminopropyltriethoxysilane(APTES) on the h-BN surface to improve the interfacial adhesion in the composite. An efficient approach was developed to functionalize h-BN with 3-Aminopropyltriethoxysilane (APTES) by wet solution method. The exfoliated h-BN was first treated with molar solutions of H2SO4/HNO3 to attach the epoxide groups on the surface of h-BN. The functionalization was confirmed by Fourier transformed infrared spectroscopy. The FT-IR peaks obtained at 1021cm(-1), 1110cm(-1) about Si-O-Si peaks and 3412cm(-1) about -NH peak. Furthermore, the introduction of APTES treated h-BN in epoxy matrix significantly enhanced the thermal conductivity at high volume fraction. The in-plane thermal conductivity at high fraction of h-BN (10 vol. %) was improved up to 2.98 W/m.K, which was ~15 times higher than that of controlled epoxy (0.2 W/m.K).