In this study, the soluble microbial product (SMP) in an anaerobic membrane bioreactor (AnMBR) was fractionated into six kinds of hydrophilic or hydrophobic fractions through a sequence of adsorption/desorption using DAX-8, Amberlyst^® 15 and Amberlyst^® A21 resins. The hydrophilic neutrals (HIN) was found to be the major component in the SMP, accounting for 74.84% in terms of the total organic carbon (TOC). Polysaccharides, protein, and humic substrates were identified in all the six types of organic fractions. In order to further understand the membrane fouling mechanism of different organic fractions, the fouling propensity was evaluated through a series of batch microfiltration experiments with a stirred dead-end filtration cell under constant pressure. The membrane suffered a quickest flux decline with the hydrophilic base (HIB) solution, next came the HIN solution and hydrophobic acid (HOA) solution. An exponential correlation was found between the flux decreasing rate and mean particle size of the organics (R²=0.9965). Classic filtration models were employed for further analyses of the fouling evolution. The standard blocking, intermediate blocking and cake filtration models were found to fit the HOA, HIN, and HIB filtration behaviors, respectively. The irreversibility of membrane fouling caused by different organic matter was also investigated. The HIN-based fouling was found to be more difficult to be cleaned than other fouling types.