This study investigates the phase evolution of ternary Zn–Ti–O nanomaterials by high-temperature annealing of ZnO–TiO2 core shell nanowires at 800 °C–1000 °C. Scanning electron microscopy images show the surface morphology of the nanowires becomes rough with an increase in annealing temperature. Moreover, X-ray diffraction (XRD) patterns and transmittance electron microscopy (TEM) analysis show that multiple Zn–Ti–O ternary compounds exist in the high-temperature annealed ZnO–TiO2 nanocomposites. These are Zn2TiO4 and ZnTiO3. The nanowires annealed at 800 °C form hexagonal ZnTiO3 and cubic Zn2TiO4 mixed phases. When the annealing temperature reaches 1000 °C, a pure and efficient crystalline Zn2TiO4 phase is obtained in the nanowires. The experimental results herein demonstrate that the annealing temperature is a substantial factor dominating the phase evolution of Zn–Ti–O ternary compounds in the solid-state reaction between the ZnO core and TiO2 shell nanolayers.