Abstract: The effect of hydrophobic and hydrophilic fractions on membrane flux is investigated by DAX-8 resin for fractionation. The results show that hydrophobic fraction resulted in rapid decline in flux and hydrophilic fraction resulted in slow decline. It is found that addition of 25 and 100 mg L-1 coagulant with 19.2 and 31.6% of TOC removal respectively, obvious enhancement of flux is observed. It can be concluded that the enhancement of flux is depend to a large extent on the removal efficiency of hydrophobicity by pretreatment. The more hydrophobic fraction is removed, the more flux is enhanced. The more hydrophobic fraction is rejected by UF membrane, the more flux is declined. The research also indicates that when Uftrafiltration (UF) membrane filtrates coagulate treated water, UF membrane tends to reject hydrophilicity.