One-dimensional (1D) nanostructures of Co3O4 were synthesized via a mild hydrothermal route. The results of XRD, IR, and TEM revealed a phase transformation was accompanied by the replacement of NO3− with CO32− throughout the hydrothermal process. The symmetric types and amount of NO3− and CO32− intercalated between the brucite layers played an important role in the formation of nanowires from the hydrothermal system. The amount of CO32− increased as the hydrothermal reaction proceeded. The substitution of CO32− for NO3− led to a variation of interlayer forces thus resulted in the instability of intralayer interactions. Therefore, a shape transformation from sheets to wires occurred. Upon calcination, the shapes of precursors were preserved, and 1D nanostructures of Co3O4 resulted.