ZnO micro/nanocrystals at large scale were synthesized through the thermal evaporation of Al-Zn mixtures under air atmosphere. The effect of synthetic temperature and time on the morphology of the micro/nanocrystals was examined. It was found that the temperature and time affected the morphology of the ZnO crystals. At temperatures below 900 oC, no crystals were synthesized. At a temperature of 1000 oC, ZnO crystals with a rod shape were synthesized. With an increase in temperature from 1000 oC to 1100 oC, the morphology of the crystals changed from rod shape to wire and granular shapes. As the time increased from 2 h to 3 h at 1000 oC, tetrapod-shaped ZnO crystals started to form. XRD patterns showed that the ZnO crystals had a hexagonal wurtzite structure. EDX analysis revealed that the ZnO crystals had high purity. It is believed that the ZnO nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the micro/ nanocrystals in the SEM images.