Zinc oxide (ZnO) nanorods (NRs) with various aspect ratios (by changing the growth time between 0-240 min) were synthesized using hydrothermal method and were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and UV–Visible and photoluminescence (Pl) spectroscopies. It was found that growth timeis directly related to the length, orientation and aspect ratio of the NR arrays. The optical transmittance of NR arrays indicated a regular decrement of average transmittance with increasing the length and aspect ratioof the NRs in the visiblerange. The porous ZnOnanorod grown for 240 min with the thic ness of 1.56 µm and texture coefficient of 0.96 exhibits some interesting properties li e average visible transmittance of 60%, refractive index of 1.34, pac ing density of 0.26 and lowest optical band gap. As the growth time increased, the PL intensity sustained a general wea ening and a red-shift of UV-emission pea position. The UV-assisted photocatalytic degradation of 4-Nitrophenol (4-NP) of ZnO NRs were investigated. The considerable photocatalytic performance of ZnO NRs with highest aspect ratio was explained by its porosity and optical characteristics.