The influence of particle shape and surface roughness on the rheological properties of cementitious composites (cement paste plus coarse and fine particles) was investigated for mixtures of mortars and laboratory-made aggregates. The coarse particles were monosized spheres and cubes made from mortar, and monosized glass spheres, uncoated or roughened. The fine particles were uncoated or roughened monosized glass mini-spheres. The coarse particle mixtures were tested with a concrete rheometer to investigate separately the influence of overall particle shape and surface roughness on rheological properties as a function of aggregate concentration. The fine particle mixtures were tested with a paste rheometer to investigate the effect of surface roughness on flow at a smaller length scale using a different rheometer size and geometry. Results showed that shape had a large effect on plastic viscosity and, to a lesser degree, on Bingham yield stress. Surface roughness did not appear to have a significant effect on either property at the scale of roughness and particle volume fractions used. The tests were simulated using a validated computer model, which showed good agreement with the measured results. (C) 2008 Elsevier Ltd. All rights reserved.