Magnesium oxide coated multiwalled carbon nanotubes (MgO@MWNT) were fabricated and dispersed into epoxy matrix. The microstructures of MgO@MWNT and epoxy/MgO@MWNT nanocomposites were characterized by TEM and SEM. Electrical resistivity and thermal conductivity of epoxy nanocomposites were investigated with high resistance meter and thermal conductivity meter, respectively. MgO@MWNT has core-shell structure with MgO as shell and nanotube as core, and the thickness of MgO shell is ca. 15？nm. MgO@MWNT has been dispersed well in the epoxy matrix. MgO@MWNT loaded epoxy nanocomposites still retain electrical insulation inspite of the filler content increase. However, thermal conductivity of epoxy was increased with the MgO@MWNT content increasing. When MgO@MWNT content reached 2.0？wt.%, thermal conductivity was increased by 89% compared to neat epoxy, higher than that of unmodified MWNT nanocomposites with the same loading content. 1. Introduction Integrated circuit with high integration and miniaturization has resulted in a large amount of waste heat that is produced when electronic components work at high frequency. Accumulated heat should make semiconductors’ working stability poor and life expectancy short under higher thermal environment [1]. High performance of electronic packaging material is expected to transport the heat to the integrated circuit [2]. Traditionally, some microsize fillers with high thermal conductivity have been added into polymer matrix to obtain electronic packaging materials [3–5]. However, high content of filler makes mechanical properties of composites deteriorate. Carbon nanotubes (CNT) have ultrahigh thermal conductivity, such as single-walled carbon nanotubes (SWNT) with 6000？W/(m·k) and multiwalled carbon nanotubes (MWNT) with 3000？W/(m·k) [6, 7]. Theoretically, small amount of CNT added can sharply improve the thermal conductivity of polymer matrix [8]. In fact, thermal conductivity improved by CNT is very far below the expected value, which results from the interface thermal resistance between CNT and polymer [9]. The interface thermal resistance weakened the heat flow transporting in the composites. To decrease thermal resistance and enhance heat flow transporting in the interface of CNT and polymer, some researches focused on the interface design between carbon nanomaterial and polymer to improve the thermal conductivity or other properties of polymer composites [10–14]. Although CNTs can improve the thermal conductivity of polymer, their excellent electrical conductive property can significantly change the electric
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