In this paper, the hydrothermal processing (HTP) was employed to synthesize Zinc oxide nanorods (ZnO-NRs) arrays on p-type Si(100), and glass substrates at 95℃, and 120 ℃. The X-ray diffraction(XRD) measurements confirm that all prepared films are polycrystalline with hexagonal structure and orientation on plane c-axis (002) as shown in FESEM images. The intensity of peak (2ө =34.2°) was increased and its full width at half maximum (FWHM) decreased with the increase of temperature due to the increase in their particles size. The images of field emission scanning electron microscopy (FESEM) show that ZnO-NRs on Si substrate gives a better result from the glass substrate with an aspect ratio (17.95, and17.43) for the prepared samples at (120°C, and 95°C) , respectively. The growth temperature effect is clear onto average diameter, average length and aspect ratio, where they increased with increasing temperature. The optical measurement shows that the peak of absorption increased with increasing temperature while the reflection spectra decreased. The band gap of ZnO-NRs on Si was determined from the reflection spectra while for glass substrate was determined from absorption spectra.