Epoxy resin nanocomposites suspended with carbon nanofibers (CNFs) have been prepared. A bifunctional coupling agent, 3-aminopropyltriethoxysilane, is used to treat the acid oxidized fibers. The dispersion quality of the CNFs with and without surface modification is monitored by an oscillatory rheological investigation. The addition of fibers is observed to influence the rheological behaviors of the suspensions drastically. Newtonian fluid behavior disappears as the fiber loading increases. A significant increase of the complex viscosity and storage modulus is observed, especially when the temperature increases to 50 degrees C and 75 degrees C. In-situ reaction between the amine-terminated functional groups on the silanized fibers and the resin, is justified by the FT-IR analysis and is responsible for the improved fiber dispersion and network formation. A decreased rheological percolation is observed after silanization due to the improved fiber dispersion quality. The electrical conductivity percolation is well correlated to the rheological percolation for the as-received fiber resin suspensions. However, with an insulating organic coating on the fiber surface, the conductivity increases slightly and lacks the correlation to the rheological percolation. (c) 2010 Elsevier Ltd. All rights reserved.