An alternative ultrafiltration membrane integrity test was already developed in laboratory scale. It is based on the use of magnetic nanoparticles (Fe3O4) and measurement of magnetic susceptibility. The mean size of nanoparticles used is around 35 nm and they show a good disparity between 20 and 100 nm. In this paper, validation of this membrane integrity monitoring method was achieved by industrialscale tests. Two holes with 0.6 mm internal diameter in a module containing 10 000 fibers (35 m2 surface area) was efficiently detected by injecting 750 mL of 1.7 g.L−1 nanoparticle solution during 2s when the test was operated at low TMP (0.096 bar, corresponding to a flux of 2.2 m3.h−1). In addition, it has been demonstrated that within the detectable range, this membrane integrity test with magnetic nanoparticles has a very rapid response time. The response time depends on the permeate flux and the dead-volume of the pilot. This membrane integrity test, with the advantages of on-line operation, high detection sensitivity, detection specificity and very low influence on membrane fouling, seems to be suitable for large scale drinking water plants.