In this study, a novel multifunctional poly(arylene ether nitriles)(PEN)/carbon nanotubes/Fe3O4 nanocomposite with high tensile strength, magnetic, and electrical properties was investigated. First, we synthesized the monodisperse Fe3O4 nanoparticles on the surface of the multiwalled carbon nanotubes and then the hybrid material was compounded with PEN through the solution-casting method. The SEM and TEM images indicated that the monodisperse Fe3O4 nanoparticles, with the diameters of 70 similar to 80 nm, were self-assembled along CNTs via the covalent bond method, which was confirmed by FTIR and XRD. The results of tensile properties showed that the tensile strength and modulus reached their highest values at the CNTs/Fe3O4 loading content of 1 wt % and both were greatly enhanced after heat treatment. Electrical conductivity of the polymer was dramatically enhanced at the low loading level of CNTs/Fe3O4; the electrical percolation of was in the range of 5 similar to 8 wt % of CNTs/Fe3O4. The magnetic study showed that the saturation magnetization (Ms) of PEN/CNTs/Fe3O4 nanocomposites increased with the increase of CNTs/Fe3O4 loading content, and the coercive force (Hc) of the nanocomposite was independent of the CNTs/Fe3O4 content. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 611-619, 2011