Biodiesel is currently getting great attention because it can reduce carbon dioxide emissions by 78.5% compared to petroleum-based diesel. The reaction that can produce biodiesel is the esterification reaction with the addition of a heterogeneous catalyst, one of which is SnO₂ which can be used as Lewis acid for the esterification reaction. In our study, SnO₂ has been successfully synthesized and then succeeded in reducing the level of oleic acid FFA (Free Fatty Acid) through an esterification reaction. SnO₂ was synthesized from SnCl₂.2H₂O using the hydrothermal method with the addition of CTAB (Cetyl Trimethyl Ammonium Bromide) as a capping agent which was then analyzed using XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy). The catalytic activity of the SnO₂ sample was carried out through the esterification reaction of oleic acid in ethanol at 65 °C for 6 hours with variations in catalyst weight and variations in the ethanol mole ratio. From XRD analysis, SnO₂ sample consists of cassiterite minerals and has typical peaks at 2θ = 26.56°; 33.84°; 37.92°; 38.90°; 42.53°; 51.64°; 54.66°; 57.76°; 61.68°; 62.34°; 64.60°; and 65.88° with the highest intensity at 2θ = 33.84°. During condition optimization of esterification reaction of oleic acid, variations in the weight of SnO₂ catalyst resulting from the optimum FFA level could be reduced by 75.05%, whereas to variations in the mole ratio of ethanol, the optimum FFA level could be reduced by 85.53%. In our study, SnO₂ has been successfully synthesized and then succeeded in reducing the level of oleic acid FFA through esterification reaction until 85.53%.