Abstract: Multiwall carbon nanotubes (MWCNTs) were modified in three ways, namely, oxidizing with HNO3, filling with Ag, and grafting with hexamethylene diamine. Epoxy/modified MWCNTs composites were prepared and its thermal conductivity was tested. TEM images showed that the modified MWCNTs were dispersed in the epoxy matrix homogeneously. The thermal conductivity was improved obviously. As the modified MWCNTs was 2.2 %, the thermal conductivity of the composites containing Opened MWCNTs or Ag-filled MWCNTs reached 0.20 W/(m·K), 33.3 % higher than that of neat epoxy resin.