Highly crystalline CoO and Co₃O₄ nanowires were prepared by vapor-phase conversion of ZnO nanobelts. The ZnO nanobelts were successfully transformed into highly crystalline CoO nanowires by thermal evaporation of CoCl₂ at 700 °C in Ar, which were subsequently converted to Co₃O₄ nanowires by oxidative annealing at 600 °C. The reactions at 500 and 550 °C in 0.5% O₂ led to the formation of well-defined oxide p–n junction nanostructures such as Co₃O₄-decorated ZnO nanobelts and ZnO–ZnCo₂O₄ core–shell nanocables, respectively, as the reaction intermediates. The evolutions of phase and residual Zn component during the conversion were investigated in relation to the reaction temperature and oxygen partial pressure.