The fouling of ceramic ultrafiltration membranes by protein under dynamic filtration conditions has been investigated by small angle neutron scattering(SANS). Bovine serum albumin (BSA) solution was pumped through a thin commercial alumina membrane in a quartz cell specially designed to allow simultaneous SANS. SANS from clean membranes immersed in D2O obeyed Pored＇s law and showed that the pores in these ultrafiltration membranes more closely resemble fractal or random pore structures than well-oriented monodisperse arrays of cylindrical pores. During protein filtration, the SANS patterns showed a buildup with time of protein on all parts of this internal surface; The effects of time and pH indicate that the performance with respect to filtration is closely linked to the buildup of the adsorbed layer of protein.