It is a great challenge for facile fabrication of thermal materials with both high thermal conductivity and excellent mechanical behaviors. Here, using tannic acid (TA) as a surface modifying agent, few-layer boron nitride nanosheets (BNNS) were effectively obtained by exfoliation of h-BN microplatelets through wet ball-milling. The existence of TA on the surface of BNNS also increased the dispersibility and stability in aqueous solution. By means of vacuum filtration of the dispersion of graphene oxide (GO) and BNNS, layered composite films of GO/BNNS were fabricated easily and at low cost. Because of the orderly orientation of GO and BNNS along the horizontal direction and high inherent thermal conductivity of the nanosheets used, a high in-plane thermal conductivity of 11.9 W/mK was reached with 80 wt% of BNNS. We also found that the thermal conductivity of the film could be further enhanced through adding 1.6 wt% PVA in the system to fill the voids between the nanosheets. The resulting composite film also exhibited excellent tensile strength of 41.0 MPa, flexibility potential for utilization on a curved surface, and electrical insulation up to 6.8 x 10(9) Omega cm.