The purpose of this study is to investigate the defects optical and gas sensing properties of  ZnO nanorods. ZnO nanorods have a high surface-to-volume ratio, making them ideal for sensing applications in addition to their well-known physical and optical features. The unique morphology and structure of the nanorods, which are impacted by the seed layer features, provide enhanced sensing capabilities. In this study an vertically oriented zinc oxide (ZnO) nanorods array were hydrothermally produced at 60°C, on thin seed layer of ZnO which was fabricated using 2-methoxy ethanol and zinc acetate as a precursor mixture, and ethanolamine as a stabilizing. A basic simple inexpensive technique, sol-gel drop cast method was used for ZnO thin film that was deposited on glass substrate that was used as seed layer for nanorods using precursor mentioned. The precursors for nanorod were zinc sulphate (2 M aqueous solution) and ammonium chloride, with adjusted pH (~11) by using sodium hydroxide. Ammonium chloride functions as a catalyst in the mixture, facilitating the anisotropic development of ZnO nanorods. Scanning electron microscopy (SEM), and sensing properties of nanorods measured by the fabricating a MSM structure using hard mask. Energy band gap of the nanorods where studied by using the UV method and theoretically using DFT theory run on Quantum Espresso software. The experimental and theoretical results were in agreement.