The influence of primary particle size distribution (PPSD) on aggregation behaviour and the resulting effect on yield stress of a concentrated colloidal suspension was investigated theoretically. The discrete element model (DEM) combined with the well-known DLVO theory was employed to obtain an insight into the aggregation process of nanoparticles with different PPSDs, where a modified version of the Flatt and Brown model [J. Am. Ceram. Soc. 89 (2006) 1244-1256] [9] was employed to calculate the corresponding suspension yield stress from the simulation results. Specifically, the aggregate growth and structure in terms of fractal dimension, coordination number and the longest dimension were examined. It was shown that at small PPSD variances, a netlike structure was formed with aggregate branches interconnected in multiple locations, whereas at large variances aggregates with more compact structure and smaller longest dimension were generated. The rate of aggregation and particle assemblage was found to be faster at broader PPSDs, in turn generating aggregates with narrower size distributions and more compact structures. The influence of PPSD on coordination number (CN) was found to be minor while a decrease in PPSD variances led to an increase in both the mass-equivalent size and the longest dimension of aggregates. Further, suspension yield stress decreased as PPSD became broader. The simulation results agreed well with the experimental measurements and the published data. (C) 2011 Elsevier B.V. All rights reserved.