The aim of this investigation was to study the kinetics of readily biodegradable soluble substrate, and the interactions between the bioflocculation process and such kinetics. Several batch test experiments were performed at different soluble-substratebiomass ratios in order to evaluate its impact on the kinetics and the order of the reaction. Similarly the consumption of dissolved substrate was compared using two different bacterial suspensions: (1) flocculated suspension; and (2) dispersed cells suspensions. In this research flocculated biomass from a complete mixed activated sludge (CMAS) system was tested using sequencing batch reactors (SBR). Results indicate that when the So/Xo ratio is low (below 0.3) the removal of readily biodegradable soluble substrate can be well described by first-order kinetics with an asymptotic non-biodegradable portion for both flocculated and dispersed cells suspensions. However, it was found that the dissolved COD consumption for freely dispersed cells proceeds at a faster rate than for flocculated suspensions.