The layer-by-layer (LbL) assembly of polyelectrolyte multilayers on to a porous supporting membrane is able to create various new composite membranes. However, the low efficiency and long time required for such procedures limit practical applications. In this study, an automatic spray system has been constructed for the rapid assembly of polyelectrolyte multilayers on to nanoporous supporting membranes. The compounds polyacrylic acid and poly(ethyleneimine), used as a model polyelectrolyte pair, were alternately sprayed on to a polyacrylonitrile ultrafiltration membrane. Experiments proved that the composite membrane obtained in this way had a good pervaporation dehydration performance. In addition, the process times were dramatically decreased, by as much as 80 folds, when compared with classical dip-LbL methods. Such an automated system can easily be converted to the assembly of various organic species. Therefore, it is a versatile and highly efficient system for manufacturing composite multilayer membranes for many separation applications. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 250-257, 2013