Nanostructured zinc oxide (ZnO) materials have received considerable interest from scientists due to their remarkable performance in electronics, optics and photonics. ZnO nanoparticles were synthesized by co-precipitation method. ZnO nanoparticles were synthesized using Zn(NO3)3 and K2CO3 precursors. The structure of the obtained product was confirmed by the powder X-ray diffraction (XRD) analysis. The morphology, size and structure of the as prepared ZnO nanoparticles were investigated using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) analyses. The composition of nanocrystals was determined by electron dispersive spectroscopy (EDS). XRD pattern showed that the zinc oxide nanoparticles exhibited hexagonal wurtzite structure. By SEM images, multiple layered structure of ZnO nanoparticles were observed after calcinations. The particles size were measured in the range of 20-80 nm for sphere-like shaped as-synthesized ZnO and 40-100 nm for pyramid-like shaped annealed ZnO with less agglomeration, as estimated by XRD technique and direct HRTEM observation. The EDS spectrum showed peaks of zinc and oxygen free of impurity.