The effects of polymer flocculants on coagulation/flocculation-microfiltration of two surface waters were investigated in terms of turbidity, dissolved organic matter concentration and molecular characteristics. The results showed that all polymers studied improved the dissolved organic carbon removal by polyaluminum chloride coagulation, but only cationic polymers improved UV (254) removal. High performance size exclusion chromatography analyses showed that cationic polymers slightly increased removal of small UV absorbing matters in the molecular weight range of 1100 to 4000 Da compared to 4000-9000 Da by polyaluminum chloride only. These impacts have significant implications in the membrane fouling potential and permeate water quality of the pretreated water.