Nanocrystalline ZnO ceramics with grain sizes of ∼100 nm were prepared by pressureless sintering at 800°C for 2 h and spark plasma sintering (SPS) at 550°C for 2 min, respectively. Excellent green emission properties were obtained in the ZnO ceramic prepared by the SPS process and in the pressureless-sintered ZnO ceramic prepared at 1000°C for 2 h, which are attributed to the vacuum ambience of the SPS process and the sublimeness of the interstitial Zn at >900°C in air, respectively.