Biodiesel is considered a renewable, sustainable, and friendly energy source that can replace fossil fuels. Biodiesel can be produced either by esterification of fatty acids or transesterification of triglycerides. In this study, crab shell was recycled as the CaO source. CaO was combined with SiO₂ from rice husk to form a novel heterogeneous catalyst for the esterification. The catalyst characterization was studied by TGA, XRD, FT-IR, and SEM-EDX methods. Synthesized CaO and CaO-SiO₂ were applied for the esterification of oleic acid. The effects of catalyst, temperature, reaction time, and MeOH:oleic acid molar ratio were investigated. The results revealed that the addition of SiO₂ can enhance the reaction rate. The reaction temperature and time affected oleic acid conversion more significantly than MeOH:oleic acid molar ratio. The highest conversion (78.49%) was achieved at 68°C, 7h, 10wt% CaO-SiO₂ (900°C) catalyst, and 10:1 MeOH:oleic acid molar ratio.