The fractionation of 2 wt% gum arabic using 0.1, 0.5 and 0.8 μm polysulfone (PS) flat sheet membranes is investigated. Fluxes of between 35 and 80 L m−2 h−1 were achieved during diafiltration experiments at cross-flow velocities of between 1.0 and 1.6 m s−1. Although all three membranes rejected a large proportion of the total solids, a high degree of fractionation was seen, particularly for the 0.1 μm membrane, which establishes the principle of this novel membrane application. Rejection of high MW arabinogalactan-protein complex (AGP) was observed with selective transmission of lower MW glycoprotein (GP). Multi-cycle experiments showed that flux can be well recovered after cleaning of the membrane, although with the 0.8 μm membrane, greater fractionation was seen after some fouling had occurred.