In this study, pretreatment of organic matters with $MIEX^{(R)}$ was evaluated using bench-scale experimental procedures on four organic matters to determine its effect on subsequent UF membrane filtration. For comparison, coagulation process was also used as a pretreatment of UF membrane filtration. Moreover, the membrane fouling potential was identified using different fractions and molecular weights of organic matters. From the removal property of MW organic matters by coagulation process for the sample water NOM and AOM, the removal efficiency of high MW organic matters were much higher than those of low MW organic matters. It was shown that the removal efficiency of high MW organic matter more than 10 kDa was lower than that of low MW organic matter for $MIEX^{(R)}$ process. For the change of permeate flux by the pretreatment process, $MIEX^{(R)}$+UF process showed high removal efficiency of organic matter as compared with coagulation-UF processes, but high reduction rate of permeate flux was presented through the reduction of removal efficiency of high MW organic matter. From sequential filtration test results in order to examine the effect of MW of organic matter on membrane fouling, it was found that the membrane foulant was occurred by high MW organic matter, and the DOC of organic matter less than 0.5 mg/L was working as the membrane foulant. In the case of sample water composed of low MW organic matter less than 10 kDa, since the low MW organic matter less than 10 kDa has high removal efficiency by $MIEX^{(R)}$, low reduction rate of permeate flux is obtained as compared with coagulation-UF processes. In summary, it is required to conduct the research on physical/chemical characteristic of original water before pretreatment process of membrane process is selected, and a pertinent pre-treatment process should be employed based on the physical/chemical characteristic of original water.