The adsorption of 9 species of bacteria onto laboratory-activated sludge flocs were investigated and a kinetic model describing the adsorption process was proposed in order to design an effective bioaugmentation strategy. The typical time course of bacterial adsorption, which is a triphasic process, consisted of lag, rapid adsorption, and stationary phases. The equilibrium of the cells in the stationary phase obeyed the Freundlich isotherm. The reversible and nonlinear model could describe the process to a certain degree and the Freundlich parameters and specific sorption rates were estimated for each bacterial strain. There was no apparent relationship between the estimated parameters and characteristics of the bacterial strains, such as specific growth rate, hydrophobicity of the cells, and flocculation activity against kaolin clays. However, the high hoc formation ability of the bacterial strains was observed to be related to high cell concentrations although a longer lag time was required.