The presence of soluble microbial products (SMP), including utilization-associated products (UAP) and biomass-associated products (BAP), is of great importance to membrane fouling problem. In this study, characterization and modeling of the SMP were conducted towards a better understanding of the production and composition of SMP in the membrane bioreactor (MBR). Based on the chemical analysis, both UAP and BAP exhibited the biodegradability and had a large fraction of molecular weight greater than 20 kDa, thus hydrolysis was assumed as the first step for SMP utilization. The simulation of biological processes was described on the platform of activated sludge model 3 (ASM3) with two main modifications: (i) adopting the concept of simultaneous growth and storage of organic substrates by heterotrophic bacteria; (ii) introducing the formation and degradation of SMP into the biological processes. Batch experimental results were used for SMP parameter estimations, and simulation results showed that the model was able to describe the SMP dynamics and provide further insights into MBR operations. The effect of the sludge retention time (SRT) and hydraulic retention time (HRT) on the formation of SMP could therefore be analyzed by model simulation: a minimum SMP production with 25.1 mg COD/L was suggested at 40 days SRT and 8 h HRT. (c) 2010 Elsevier B.V. All rights reserved.