Mono-dispersed ZnAl 2 O 4 was successfully synthesized by a hydrothermal method at 260 o C for 20 h. The powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential thermal analysis-thermal gravimetric (DTA-TG), and BET. The mean particle size was 482 nm with narrow distribution.