Novel organo-mineral membranes were prepared under an external orthogonal magnetic field from suspensions by the phase inversion process. The suspensions consist of polyacrylonitrile, dimethyl sulfoxide, poly( vinylpyrrolidone), and ferrosoferric oxide. The cross-section structures observed by SEM show that the magnetic field can control the alignment orientation of magnetic Fe3O4 aggregates in the membrane. Moreover, the addition of Fe3O4 can lead to the change of macrovoids in the sublayer from being tidy and perpendicular to the membrane plane to being irregular and oblique to the membrane plane. The retention rate of PAN-Fe3O4 membranes to BSA decreases with the increase of Fe3O4 amount and the changes in the retention rate are within a range of 2%. Furthermore, 1 wt % Fe3O4 added in PAN membranes may result in a decline of the membrane permeability or the antifouling performance. But the membrane permeability and the antifouling performance then increase with the increase of Fe3O4 amount from 1 to 4 wt %. Contrary to common results, the membrane permeability and the antifouling performance appear to have no direct correlation to the roughness of membrane surface obtained by AFM.