A physical-mathematical model describing the motion and collection of orientable nanoparticles from airflow in magnetic filters is developed. The particles are spheres having permanent magnetic moments. The model accounts for particles' translational and rotational Brownian motions, and their magnetic interactions. The influence of filtration operating conditions and particle diameters on their behavior and magnetic capture efficiency is investigated numerically. The results of simulations are compared with experimental data. Strong dependence of the capture efficiency on the particle diameter is found for d(p)<0.2μm. The optimal filtration parameters leading to effective magnetic capture are discussed. Copyright (C) 2000 Elsevier Science B.V.