The main focus of this study was to improve the quality of palm olein-derived used frying oil (UFO) as a feedstock for non-food applications using an adsorption process. In addition, the adsorption capability and efficiency of four different adsorbents (activated carbon, activated bleaching earth, silica gel and aluminium oxide) used in treating the oil were assessed. Silica gel, when employed at an optimum treatment level of 20%, was found to be highly effective in the overall improvement of the quality of UFO, leading to significant reductions in free fatty acids (FFA) (percentage improvement, PI = 68.5%), peroxide value (PV) (PI = 85%), anisidine value (An. V) (PI = 33.8%) and total oxidation value (TOTOX) (PI = 45.3%). In terms of adsorption capability in FFA reduction, the Freundlich adsorption isotherm of FFA indicates a similar finding, supporting the pre-treatment of UFO using silica gel with its highest adsorption capacity (K = 1.0017), followed by activated carbon and the other two adsorbents.