To determine thin films' properties of commercially available gallic acid molecule, they were deposited onto a suitable substrate using spin coater. UV-Visible absorption spectroscopy and atomic force microscopy (AFM) were employed for the characterization of the deposited thin films. Characterization results obtained by these two techniques indicated that the gallic acid molecules are suitable for transfer onto a glass or quartz substrate. Gas-sensing properties and thickness of these thin films were elucidated using surface plasmon resonance (SPR). Thickness values of spun thin films were obtained at different spinning speeds. Then, the gas-sensing properties were examined by exposing them to the vapors of four volatile organic compounds (VOCs). It was found that the spun films of this material were selective for methanol vapor yielding rapid response and recovery time and thin films of gallic acid exhibited reversible changes in the optical behavior, which makes them suitable for practical methanol-detection applications.