ZnO particles with different structures were filled into silicone oil to form a fluid system. The experimental results demonstrate that the thermal conductivity and viscosity of thermal greases depend strongly on the structures and volume fractions of ZnO. The silicone grease filled by tetrapod-shaped ZnO (T-ZnO) whiskers has the superior thermal transport property in comparison to those containing ZnO nanoparticles (ZnO-NPs) and ZnO short-columnar (ZnO-SC). The synergistic effect can be observed by mixing T-ZnO with ZnO-SC. This unique three-dimensional network of heat conducting path offered by hybrid fillers can effectively reduce phonon scattering at the interface between fillers and silicone, and improve the thermal conductivity to 0.83 W/(m.K). Additionally, a suitable model was set up to explain the thermal conductivity synergistic enhancement effect. (C) 2017 Elsevier Ltd. All rights reserved.