The hydrothermal process is considered as one of the simplest and cheapest methods applied to prepare zinc oxide nanorods (ZnO-NRs) to be arranged on glass substrates. Each glass substrate was pre-coated by ZnO seed layer. The grown nanostructures were annealed in air at temperatures of 200, 250 and 400 °C. The effect of annealing process on structural, optical and morphological properties has been studied. The X-ray diffraction (XRD) tests confirmed that all synthesized samples are polycrystalline structures that possess hexagonal shapes and preferable orientation plane of (002), along with c-axis coordination which is also evident from FE-SEM image. The intensity of (002) peak was most prominent at 250 °C. Due to the increase in crystals size with annealing temperature at 250 °C, the full width at half maximum (FWHM) has been decreased. The energy dispersive spectroscopy test (EDS) showed that the Zn:O atomic ratio for all samples was nearly stoichiometric. The atomic force microscopy (AFM) image show that the root mean square (RMS) decreases when the temperature increases up to 400 °C. The optical transparency and band gap of (ZnO-NRs) decreased with the increase of annealing temperature.