ZnO crystals with octahedral shape were synthesized by thermal evaporation technique. ZnF2 powder was used as the source material. The thermal evaporation and oxidation of ZnF2 powder was carried out for 1 hr at 1,000℃ in air under atmospheric pressure. SEM images showed that the ZnO crystals produced by oxidizing ZnF2 vapor possessed a characteristic octahedral shape. XRD spectrum revealed that the ZnO octahedron had hexagonal wurtzite structure. In the room temperature photoluminescence spectrum, a strong green emission peak at around 510 nm was observed.