Silicon carbide (SiC) nanoparticles with no surface treatment raise the viscosity of a vinyl ester resin much more intensely than micrometer-size SiC particles. An effective dispersant generally causes a reduction in the resin viscosity attributed to its surface-active properties and thereby increases the maximum fraction of particles that can be introduced. This article assesses the rheological behavior of SiC-nanoparticle-filled vinyl ester resin systems with the Bingham, power-law, Herschel-Bulkley, and Casson models. The maximum particle loading corresponding to infinite viscosity has been determined to be a 0.1 volume fraction with the (1 - eta(-1/2)(r))-phi dependence (where eta(r) is the relative viscosity and is the particle volume fraction). The optimum fractional weight percentage of the dispersants (wt % dispersant/wt % SiC) is around 40% for 30-nm SiC nanoparticles, which is much higher than 1-3% for micrometer-size particles. SiC nanoparticles at a concentration of 9.2 wt % (0.03 volume fraction) cause a fourfold increase in the resin viscosity. The addition of a dispersant at the optimum dosage lowers the viscosity of SiC/vinyl ester suspensions by 50%. The reduction in the viscosity is substantial to improve the processability of SiC/vinyl ester nanocomposites. (c) 2006 Wiley Periodicals, Inc.