In the present work, a new heterogeneous catalyst for oil transesterification with methanol has been developed. The catalyst is based on the introduction of sodium in calcined hydrotalcite. Two different raw materials have been used to determine the usefulness of this new catalyst: sunflower oil and used frying oil from a university restaurant. In this way, the efficiency of the new heterogeneous catalyst by using an urban residue was tested. Different parameters that can modify the extension of the transesterification reaction have been evaluated. Results obtained at 60 degrees C show that hydrotalcite modified with sodium presents adequate characteristics for this kind of reactions with both raw materials evaluated. An important factor observed in the present study is that no soap was formed in any of the reactions carried out, even in the case of used oil with high acid index. The iodine index of biodiesel generated with waste cooking oil presents values within the limits established by general biodiesel specifications.