Electrospinning, a general synthetic method, has been adopted to fabricate and assemble room-temperature ferromagnetic diluted magnetic semiconductor nanofibers. Employing electrospinning technique followed by calcination and annealing process, we have successfully prepared uniform Co-doped ZnO nanofibers with concentrations of Co between 0 and 15.0 at.%. And the solubility limit of Co dopant in ZnO nanofibers has been determined. The Zn1−xCoxO nanofibers annealed in hydrogen atmosphere exhibit ferromagnetism at 300 K, deviating from paramagnetism in the ones that were without annealing. Hence, the ferromagnetism in these fibers depends on not only Co addition but also the annealing process. Moreover, both coercive field and saturation magnetization increase along with the Co content. The ultimate coercive field and saturation magnetization are 610 Oe and 0.336 μB/Co of Zn0.85Co0.15O nanofibers, respectively. Origin of the observed enhanced room-temperature ferromagnetism in Zn1−xCoxO nanofibers is analyzed according to the detailed micro-structural characterization.