Nanofiltration membranes were surface modified by grafting poly(acrylic acid) (PAA) nanochains using a UV initiated free radical polymerization method. These pH sensitive membranes were then used to separate monosaccharides, disaccharides, and their mixtures from filtration feed streams. It was found that pH dramatically affects the flux, rejection, and selectivity using these modified pH sensitive nanofiltration membranes Membrane performance could be enhanced not only by the conformational changes of the grafted surface layer due to protonation and deprotonation of the acid groups on the polymer. chains but also from the different interactions between the sugar molecules and the neutral PAA chain or its negative conjugate. Classical molecular dynamics (MD) simulations were conducted to investigate the specific interactions between glucose/sucrose and the neutral/negatively charged PAA chains The simulation results show that both sugar size and PAA charge affect significantly the sugar-polymer interactions.