Abstract: Today, there is an increasing demand for sensors that includes home-security, military, industrial and clinical diagnosis. In the past, Fiber Optic based Sensor (FOS) has made profound impact due to its simple, room temperature detection and large range of detection species. In the present work, a simple optical fiber for sensing ethanol vapour was developed using borosilicate glass rod as core and Successive Ionic Layer Adsorption and Reaction (SILAR) deposited zinc oxide (ZnO) thin film as cladding materials. Structural studies carried out using X-ray Diffraction (XRD) method indicates, the ZnO film was polycrystalline hexagonal structure in nature with preferential orientation along (002) plane. Grain size obtained through line broadening technique was found to be 25 nm. The two ends of the fabricated fiber were connected to a diode laser source of 850 nm and optical power meter of 0.01 dBm accuracy as detector. The transmitted light intensity of the fabricated fiber found to changes in ethanol vapour atmosphere. The response and recovery time towards ethanol at room temperature as a function of cladding thickness and length were analysed and reported.