Biodiesel is a biodegradable fuel that originates from a variety of oleaginous raw materials, although most studies have been traditionally based on vegetable oils. Rapeseed (Brassica napus) is the raw material most widely used in the production of biodiesel in temperate climate, i.e. central Europe, due to its physical properties and the content of oleic acid of its oil. However, this plant needs nitrogen fertilization at different stages of growth to achieve an optimal oilseed production, thus increasing costs. For this reason, the aim of this work was to find out the importance of nitrogen fertilization through the study of its influence on the physicochemical properties of both rapeseed oil and its biodiesel. Rapeseed variety "Lucia'' was used to carry out this research. The oil from each sample of rapeseed was extracted using mechanical processing (cold pressed) and analyzed according to European standards. Results indicate some differences on the acid value and fatty acid composition among the samples of oil depending on the level of nitrogen fertilization. With respect to the fatty acid composition, the sample 0-0 (no nitrogen fertilization) showed a decrease on oleic acid compared to the rest of samples. With the aid of an experimental design, the optimum transesterification parameters were also determined. Results indicate that the temperature of the reaction and KOH increased for the sample 0-0, while less amount of methanol-to-oil ratio was needed. Finally the most important physical and chemical properties of biodiesel were analyzed. It may be concluded that nitrogen fertilization influences oil properties. Moreover, despite of the saving during the cultivation, when the crops are not fertilized there is a rise in biodiesel production costs due to an increase of the reaction transesterification temperature and KOH needs, besides the reduction in seeds production. (C) 2013 Elsevier Ltd. All rights reserved.