The influences of membrane operating conditions and water quality on the rejection of arsenic by a negatively charged ultrafiltration (UF) membrane were investigated through a series of bench-level experiments. In general, the trends in arsenic rejection measured by these experiments are qualitatively consistent with the Donnan theory. In particular, the presence of co-occurring divalent ions was shown to have a detrimental influence on anionic As(V) rejection. As(V) rejection by the UF membrane was also shown to be sensitive to membrane operating conditions through the phenomena of concentration polarization. The possible influence of natural organic matter (NOM) on As(V) rejection by charged membranes was also explored.