AbstractEpoxy/expanded graphite (EG) and polyester/EG composites were prepared with the aid of sonication, while epoxy/expanded‐milled graphite (epoxy/milled‐EG) and polyester/expanded‐milled graphite (polyester/milled‐EG) composites were prepared on a three‐roll paint mill. The epoxy/EG and polyester/EG composites exhibit a sharp insulator/semiconductor transition at markedly low percolation thresholds, due to the vermicular shape of EG having high aspect ratio and surface area. The morphologies of epoxy and polyester resins incorporated with EG and milled‐EG fillers were observed by scanning electron microscopy (SEM). The results of dynamic mechanical analysis of the composites reveal that both EG and milled‐EG fillers increase the Tg of the epoxy matrix. Milled‐EG increases the G′ of the epoxy matrix, while EG decreases the G′ of the epoxy matrix, due to the existence of abundant pores in EG. The milled‐EG filler has the same effect on the polyester matrix as on the epoxy matrix, but the EG filler has no significant effect on the mechanical properties of polyester matrix. POLYM. COMPOS., 26:526–533, 2005. © 2005 Society of Plastics Engineers