Noncontact atomic force microscopy (AFM) has been used to investigate the surface pore structure of eight Diaflo ultrafiltration membranes covering a range of nominal molecular weight cutoff (MWCO) from 3000 to 300,000 and manufactured from three different polymer types. Excellent high resolution images were obtained, Analysis of the pore images gave quantitative information on the surface pore structure, in particular the pore size distribution and surface roughness. Such data is compared to that obtained by other techniques. Noncontact AFM is a facile and informative means of studying the surface structure of porous materials such as synthetic membranes.