Abstract: Octadecyltrimethyl ammonium bromide (OTAB) was used as a cationic surfactant to modify micron BN platelets with an organic surface. The effects of BN surface modification on the thermal conductivity of BN/epoxy composites were studied. The adsorption of OTAB on BN surface is close to saturation at OTAB concentration of 0.6 g · L^-1. BN surface modification improves the wettability of epoxy resin on BN surface and decreases the thermal conductivity of BN. SEM and viscosity characterization show that the interfacial and compatible properties of BN/epoxy composites are improved by the surface modification of BN. Due to the decrease in interfacial thermal resistance, the thermal conductivity of the modified BN/epoxy composites is higher than original BN/epoxy composites. When the filler loading is 30% (mass ratio of filler to matrix resin), the thermal conductivity of the modified BN/epoxy composite is 1.03 W(m · K)^-1, 2.15 times of the thermal conductivity (0.48 W(m · K)^-1) of original BN/epoxy composites.