Calcium oxide (CaO) catalyst was synthesized thermally from molluscs shell. The raw material was calcined at temperature between 500 to 1000C. Both commercial CaO and CaO from combusted cockle shell were used as catalyst in the transesterification reaction. The transesterification reaction was conducted in a mixture of methanol:oil (12:1, v/v) and 8 wt % catalyst for the required reaction time was used. The content was refluxed in ultrasonic bath at 65C for 15 minutes. The non-ultrasonic reaction was performed using magnetic stirrer for 3 hours. Combustion of cockle shells at 500, 600, 700 and 800°C showed no significant difference in XRD patterns and the XRD patterns are similar to calcium carbonate (CaCO 3). The peaks correspond to CaO (2θ = 32.2° and 37.4°) appeared in the XRD pattern of combusted cockle shell at 900 °C and 1000 °C, respectively. However, a peak corresponds to CaCO 3 (2θ = 29.4°) disappeared at 900 o C. These results indicate CaCO 3 transformed to CaO by combustion at or above 900°C. The percentage conversion for CaO from commercial and cockles via mechanical stirring were 96.65% and 96.77%, respectively and 88.40% and 93.33%, respectively, via ultrasonic irradiation. The percentage yield of fatty acid methyl esters (FAMEs) from both sources of CaO were found to be comparable with percentage yield of CaO from cockles which were 27.0% and 29.3% for mechanical stirring and ultrasonic irradiation, respectively. CaO from cockles shell combusted at above 900°C provides a better catalyst than commercial CaO for transesterification reaction due to the higher calcite purity.