Three identical bench-scale membrane bioreactors (MBRs) were operated to investigate the formation of effluent organic matter (EfOM) via biodegradation at different solid retention times (8, 20 and 80 days). The characteristics of organic matter in supernatants, bound extracellular polymeric substances (EPS), soluble microbial products (SMP) and effluents changed at different solid retention times (SRTs). EfOM characteristics affecting membrane fouling with respect to total hydraulic resistances and specific cake resistances were investigated using advanced organic characterization tools. EfOM characteristics determined by size exclusion chromatography with organic carbon detection, fluorescence excitation-emission matrix spectroscopy and polarity rapid assessment method were compared with the membrane fouling. In this study, a database collected from three identical bench-scale MBRs operated at different SRTs for 12 months is analyzed to investigate the intercorrelations (either positive or negative) between EfOM characteristics and membrane fouling using principal component analysis (PCA). Principal component-1 embodied the characteristics of EfOM (i.e., aliphatic biopolymers vs. aromatic humic substances), and explained 59% of the data variability. This study provides useful data on EfOM characteristics with membrane fouling, and a multivariate statistical analysis (PCA) can be used to depict the intercorrelations between EfOM characteristics and SRTs in MBRs. (C) 2012 Elsevier B.V. All rights reserved.