A membrane bioreactor (MBR) acclimatized with wastewater organic matter was employed for surface water treatment, and the feasibility of the MBR for the removal of disinfection by-product (DBP) precursors was studied. With a low pressure microfiltration hollow-fiber membrane module, a hydraulic retention time of 1.5 hours and a solids retention time of 180 days, the MBR was able to achieve 35% removal of trichloroacetic acid precursors and 21% removal of dichloroacetic acid precursors. The removal of trichloromethane (TCM) and brominated DBP precursors was unsatisfactory. The TCM yield and bromine substitution factors for trihalomethanes and dihaloacetic acids increased. The phenomena could be attributed to an extended treatment time for hydrophobic dissolved organic matter (DOM), production of soluble microbial products from biomass activities, and an increased Br/DOM ratio by the MBR. Since the MBR treatment would lead to the production of some new DBP precursors and a change of DOM composition, the toxic potency of the DBPs formed needs to be taken into consideration if this process is employed for surface water treatment.