A mathematical model is established to simulate the formation of extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (X-STO) in aerobic granular sludge. The sensitivity of these microbial products concentrations toward the key model parameters is analyzed. Independent experiments are conducted to find required parameter values and to test its predictive ability. The model is evaluated by using one-cycle operating experimental results of a lab-scale aerobic granule-based sequencing batch reactor (SBR) and batch experimental results. Results show that the model is able to describe the microbial product dynamics in aerobic granules and provide further insights into a granule-based SBR. The affect of the initial substrate and biomass concentrations on the formation of microbial products in aerobic granular sludge can therefore be analyzed by model simulation. A higher substrate concentration results in a greater concentration of EPS, SMP, and X-STO. An accumulation of biomass in the bioreactor leads to an increased production rate of EPS, SMP, and X-STO. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 546-559, 2010