This article describes a new and efficient procedure for removing Ca2+ present in biodiesel prepared using CaO as a catalyst. Washing of CaO-derived biodiesel with a boiling methanol-Na2CO3 mixture followed by a further rinsing step with water results in the effective removal of Ca2+ to levels below 5 ppm, which is the value required by most regulations. Na2CO3 is easily separated from the biodiesel by filtration. The Na+ content of the final biodiesel is also below 5 ppm, which is the value required by regulations for this ion. Rinsing only with water or with aqueous HCl without Na2CO3 treatment did not remove Ca2+ to a level below the specifications. When CaO-derived biodiesel was rinsed with sulphonic resins followed by a water washing step, Ca2+ was efficiently removed, but the acid value parameter of the final biodiesel did not meet the regulatory standards. We have also demonstrated that the synthesis of biodiesel and the removal of Ca2+ and Na+ to levels below 5 ppm can be simultaneously achieved if Na2CO3 is initially incorporated in the CaO-methanol-sunflower oil mixture used as the starting material. (C) 2011 Elsevier Ltd. All rights reserved.