The cobalt-assisted hydrothermal/solvothermal carbonization of furfural has been developed into a facile and versatile strategy to prepare structured carbonaceous materials. In this paper, the hierarchical flower-like, honeycomb-like, and spherical particles can be readily obtained in the presence of different cobalt compounds. Also, it was demonstrated that the developing of hierarchical carbonaceous structures was strongly influenced by the formation of cobalt crystals in products during the reaction. We believe that the cobalt crystals could act as a kind of structure-directing agent to induce the fabrication of hierarchical carbonaceous structures. Organic cobalt compound was indicative of beneficial cobalt precursor for synthesis of hierarchical carbonaceous structures. The presence of ethanol facilitated the aggregation and assembly of primary nanoparticles to form hierarchical structures.