Flocculation is a key unit operation in many solid-liquid separation processes, especially in wastewater treatment and mineral ore processing. At present, many attempts of flocculation process enhancement may be found in literature. One of them is an ultrasonic conditioning of polymer solution which, among the others, reduces the time needed to achieve the steady state. In this paper a semiempirical model quantifying the effect of flocculant sonication on floc growth kinetics occurring in an agitated vessel is proposed. The model is validated on the basis of experimental research made in a laboratory setup for on-line analysis of particle size distribution. Four different commercially available flocculants were sonicated and used in experiments with a model suspension of commercial chalk dust in distilled water and industrial suspension of ultrafine coal particles. It was proved that the effect of flocculation time and sonication volume energy density on floc size cannot be decomposed into two separated effects. This model may be used for the coarse estimation of other factors' impact on the course of aggregation and breakage processes. (C) 2012 Elsevier B.V. All rights reserved.