Carbon nanofibers with high surface area can be synthesized in a simple one-step reaction under relatively mild conditions using unsupported SnO-doped Fe3C catalyst. The highest activity and carbon fibers with high surface area were obtained with catalyst prepared by direct precipitation. Over this sample, selectivity of carbon deposit formation was close to 100%. It was concluded that the interaction of the two phases might be responsible for the catalytic activity, while the method of dispersal seemed to be important for the quality and surface area of the carbon deposit.