Organic matter in the tap water was isolated into strongly hydrophobic acids, weakly hydrophobic acids, charged hydrophilic and neutral hydrophilic by DAX-8, XAD-4 and IRA-958 synthetic resins. Filtration tests using polyvinylidene fluoride (PVDF), polyethersulphone (PES) and cellulose acetate (CA) membranes were conducted to investigate the contribution of different organic fractions to membrane fouling. The results show that in filtration of raw water, flux declines with PES, PVDF and CA membrane are 67%, 59% and 19% of the initial flux, indicating that the more hydrophobic membrane resulted in more severe fouling. For the effect of different fractions on flux, flux decline with neutral hydrophilic is 41%-75% of the initial flux, whereas weakly hydrophobic acids is 6%-33%, suggesting that neutral hydrophilic has a great impact on filtration flux. Among three membranes tested, CA membrane shows the lowest flux decline compared with other membranes in spite of rejection of as high as 14.69% of neutral hydrophilic, suggesting that the extent of flux decline may not be associated with the total amount of NOM removed. The mechanism of fouling was discussed and found that the neutral hydrophilic fraction with greater than 3 x 10(4) of molecular weight caused a significant flux decline, through blocking the pore for the MF or UF having greater relative molecular mass cut-off (MWCO), but resulted in a little impact on flux with the UF having lower MWCO, through forming cake layer on the surface of membrane due to not entering the inside of pore.