In this work the transformation process of sunflower oil in order to obtain biodiesel by means of transesterification. was studied. Taguchi's methodology was chosen for the optimisation of the most important variables (temperature conditions. reactants proportion and methods of purification), with the purpose of obtaining a high quality biodiesel that fulfils the European pre-legislation with the maximum process yield. Finally, sunflower methyl esters were characterised to test their properties as fuels in diesel engines, such as viscosity, flash point, cold filter plugging point and acid value. Results showed that biodiesel obtained under the Optimum conditions is an excellent substitute for fossil fuels.