The vegetable oil, fats and their biodiesel suffer with the drawback of deterioration of its quality during long term storage unlike petroleum diesel because of large number of environmental and other factors making the fuel stability and quality questionable. There are various types of stabilities such as oxidation, storage and thermal, playing key roles in making the fuel unstable. In the present paper the thermal stability of Jatropha curcas biodiesel (JCB) as engine fuel was studied. The thermodynamic parameter of activation energy (E-a) of the samples was determined by direct Arrhenius plot. The results show that the thermal degradation of all JCB samples can be treated as a first order reaction. It seems at this stage that the additives under study can offer a significant solution in inhibiting the degradation rate of biodiesel. The pyrogallol (PY) has been found to have more pronounced effect on the onset temperature (T-on) as well as on the E-a followed by propyl galate (PG) > tert-butyl hydroquinone (TBHQ) > butylated hydroxytoluene (BHT) > butylated hydroxyanisole (BHA). The results may have important applications in the development of JCB as engine fuel. (C) 2011 Elsevier Ltd. All rights reserved.