Low temperature decomposition of precursors usually leads to higher cobalt dispersion. In this study, we present a method to decompose cobalt precursors by using dielectric-barrier discharge (DBD) plasma without requiring a thermal calcination process. Cobalt (Co) catalysts prepared by DBD plasma were characterized by a range of techniques. The results indicate that the DBD decomposition method can not only reduce the decomposition time but also achieve an increased Co dispersion, small Co3O4 cluster size and uniform distribution compared to traditional calcination method. It was observed that the DBD-treated catalysts performed well in Fischer-Tropsch synthesis and were favorable for heavy hydrocarbon formation.