Scanning electronic microscopy (SEM) andX ray diffraction (XRD) have been applied to the study of structural and optical properties of ZnOnanocrystals prepared by the ultrasonic spray pyrolysis (USP) at different temperatures. The variation of temperatures and times at the growth of ZnO films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnOnanocrystals (NCs), as well as to vary their photoluminescence spectra.