Biodiesel produced by the transesterification of vegetable oils (VOs) has become more attractive recently because of its environmental benefits and the fact that it is made from renewable resources. In this work, an environmentally benign process for the production of biodiesel from used VOs by heterogeneous catalyst has been developed. Free fatty acids contained in used VOs, which cause several severe problems for the transesterification catalyzed by base catalyst, were converted to fatty acid methyl esters (FAME). By comparing the activities of the several heterogeneous catalysts, we developed WO3/Al 2O3 catalyst as a active and stable catalyst for the reaction. the preparation method of WO3/Al2O3 was studied and its long term activity was evaluated. The characterization of WO3/Al2O3 catalyst was performed by ICP, TPD and XRD analysis.