Batch thermal stressing experiments have been conducted to investigate thermal stability and decomposition of biodiesel fuel in the temperature range of 250-425 degrees C. It was found that biodiesel was stable below 275 degrees C and thermal decomposition took place at 275 degrees C or above. It has been clearly demonstrated that biodiesel decomposition mainly involves isomerization, polymerization ( Diels-Alder reaction) and pyrolysis reactions, and they occur in the temperature ranges of 275-400 degrees C, 300-425 degrees C and >350 degrees C, respectively. A six-lump model and a reduced three-lump model are proposed to describe the decomposition mechanism. Finally, experimental data were modeled by both reversible and irreversible general first order reactions, and it has been shown that the biodiesel decomposition kinetics can be well represented by the reversible model. The standard enthalpy of reaction for biodiesel decomposition was determined to be 80 kJ/mol. (C) 2012 Elsevier Ltd. All rights reserved.