Abstract The polymer composites of magnetic nanoparticles can be possibly used in a bulk form by preserving all the novel characteristics of magnetic nanoparticles such as superparamagnetic behavior. By introducing magnetic properties of Fe3O4 nanoparticles into polymer fibers, novel magnetic properties combine with the advantages of composite fibers such as light-weight and ease-of-use. Using dry-jet-wet fiber spinning technology, we have successfully fabricated iron oxide/polyacrylonitrile (Fe3O4/PAN) composite fibers with 10 wt% nanoparticle in the polymer matrix. Composite fiber with a diameter as small as 15 μm can achieve tensile strength and tensile modulus values as high as 630 MPa and 16 GPa, respectively. Superparamagnetic properties of Fe3O4 nanoparticles were preserved in the composite fibers with saturation magnetization at 80 emu/g and coercivity of 165 G.