Aggregation kinetics of colloidal polymeric particles in diluted dispersions was monitored in a stiffed tank coagulator using small angle static light scattering. Experimental data were evaluated to obtain two independent moments of the cluster mass distribution along the aggregation process. We applied a population balance modeling approach to early stages of aggregate growth, where breakage is not yet significant compared to aggregation, in order to simultaneously describe both measured moments of the cluster mass distribution. This approach allowed us to uniquely determine both the aggregation rate constant and the effective fractal dimension for aggregates produced during the initial growth regime in the coagulator. We also showed that, similarly as observed in quiescent aggregating systems, the power law region analysis of static light scattering data underestimates the fractal dimension of aggregates early in the course of aggregation. (c) 2005 Elsevier B.V. All rights reserved.