Hexagonal boron nitride (h-BN) is an ideal candidate material for electrical and electronic systems due to its excellent performance. However, the addition of platelet-like h-BN leads to a dramatic increase of viscosity of composites and anisotropic thermal conductivity of composites. Herein, modified h-BN (m-BN) was coated onto spherical α-Al 2 O 3 via chemical adhesive, and coreshell structured hybrid spherical filler (m-BN@Al 2 O 3 ) was prepared. Furthermore, the microstructure, rheology, mechanical properties, and thermal conductivity of hybrid filler/polydimethylsiloxane (PDMS) were studied. At 60 vol % filler loading, the thermal conductivity of m-BN@Al 2 O 3 /PDMS is up to 2.23 WÁm À1 ÁK À1 , which is 86% higher than that of Al 2 O 3 /PDMS and the ratio of in-plane diffusivity to through-plane diffusivity decreases from 2.0 to 1.0. At meanwhile, the viscosity of m-BN@Al 2 O 3 /PDMS is about one fourth of the viscosity of m-BN/Al 2 O 3 /PDMS. This simple and versatile strategy opens a pavement for enhancing the thermal conductivity of polymer and has great potential in high-frequency communication.