The morphology and thermal stability of bead-free and uniform electrospun pure polystyrene (PS) and PS/Ni nanocomposite fibers are investigated by SEM and TGA/DSC. A higher thermal stability is observed after introducing the nanoparticles in the polymer fibers. FT-IR analysis indicates a physical entanglement rather than chemical bonding between the nanoparticles and the polystyrene matrix. The nanoparticles still exhibit superparamagnetic properties even after dispersing in the polymer matrix, different from the reported enhanced coercivity as a result of the enlarged particle distance. However, the magnetic field required to saturate the magnetization is significantly reduced. A further oxidation is deduced after the high voltage electrospinning process.