Abstract: This study reports the synthesis of ZnAl2O4 (ZAO) nanocrystallites with various degrees of crystal quality using high-temperature annealing of efficiently cross-linked ZnO–Al2O3 core–shell nanowires. The effects of annealing temperature on the formation of ZAO nanocrystallites from ZnO–Al2O3 core–shell nanowires were investigated. X-ray diffraction patterns revealed the cubic spinel phase structure of the ZAO nanocrystallites. Scanning electron microscopy images revealed that the ZnO–Al2O3 core–shell nanowires annealed at a high temperature exhibited a rugged surface, which is associated with the formation of the ZAO phase. Transmittance electron microscopy analysis showed that the crystalline quality of each ZAO nanograin formed at 800 °C was inhomogeneous, and most of the ZAO phase exhibited unsatisfactory crystalline quality; however, those formed at 1000 °C exhibited excellent crystalline quality. The nanowires annealed at 1000 °C exhibited a strong UV band emission (3.25 eV), as well as a marked visible emission band at 2.75 eV.