Atomic force microscopy has been used to quantify surface morphology, pore size distributions and particle adhesion for three nanofiltration membranes. It was found that the mean pore diameters were similar to 1 nm and that the relative sizes corresponded to measured separation performance. Adhesion of polystyrene particles was greater than that of silica particles, due partly to greater electrostatic double-layer repulsion between the negatively charged membranes and silica, and partly to short-range repulsive interactions associated with the silica surface. It is likely that short-range repulsive interactions are also responsible for the low adhesion of the negatively charged silica particles even at the membrane which was positively charged.