The problem of a membrane air separation in the presence of a magnetic field, is considered. The membranes filled with neodymium powder, and magnetized, were made. The magnetic induction of about 0.3 mT was achieved. The Smoluchowski equation for oxygen, and simple diffusion equation for nitrogen behaviour in the air have been used, and discussed. The discussion on some mathematical variation of an analytical description of a system in question, is provided. The verification of theoretical and numerical predictions by the preliminary experimental data, is also presented. (C) 2007 Elsevier B.V. All rights reserved.