Haloacetic acids, disinfection byproducts (DBPs) formed during drinking water chlorination process are carcinogens. The efficacy of nanofiltration (NF) was examined for the removal of five regulated haloacetic acids (HAA5): chloro-, dichloro-, and trichloro-acetic acid (CAA, DCAA, and TCAA); bromo-, and dibromo-acetic acid (BAA, and DBAA) in synthetic water. NF with the dense negatively charged membrane (ES 10), is the most efficient in removing HAA5 than the loose negatively charged membrane (NTR 7410) and neutral surface membrane (NTR 729HF), due to the greater electrostatic repulsion (Donan exclusion) and sieve effect. Excellent HAA5 removal efficiency of 90%-100% could be obtained even at a low pressure of 1 x 10(5) Pa with ES 10. Changes in cross-flow velocity did not effect the performance of membranes with a small pore size such as ES 10 and NTR 729HF. The increase in HAA5 concentration exhibited the adverse effect on the performance of three membranes by strengthening the concentration polarization, which was the driving force for the diffusion of HAA anions across the membrane.