Over the years, transformer oil has been used in majority of the power transformers to provide a reliable insulating system that is effective against dielectric stresses. Oxidation often occurred in transformer oil in the presence of oxygen and moisture which will affect the stability and insulating properties of the oil. The oxidation process cannot be eliminated but it can be delayed with the presence of inhibitor content. Even though inhibitor content can reduce the oxidation rate, the amount of inhibitor content still depletes over time. Thus, a monitoring system to detect the inhibitor content concentration is very crucial as it will be able to prolong the life span of the transformer. This paper focuses on the optical characterization of inhibitor content in transformer oil by utilizing the ultravioletvisible (UV-Vis) spectroscopy technique. It was found that oil samples with inhibitor content produce multiple absorbance peaks in the range of 350 nm to 500 nm. A clear difference in peak absorbance near 450 nm indicates the difference in the inhibitor content concentrations. Based on the results of this work, a portable and low cost optical sensing device can potentially be developed for the detection of inhibitor content in transformer oil using UV-Vis spectroscopy.