The thermal decomposition of lithium hexafluorophosphate was studied by using C80 calorimeter, and the samples were heated at a 0.2 K-min(-1) heating rate from ambient temperature to 573 K in pressure-sensitive transducer fitted and sealed vessel with argon atmosphere. It is found that LiPF6 decomposes near 433 K, and the gas product PF5 causes the pressure increasing. The LiPF6 decomposition reaction order is calculated based on the pressure data by two methods, its average value is n = 1.5, then, the reaction is assumed to be dependent on the Arrhenius law and mass action law, and thus the activation energy and pre-exponential factor were calculated to be E = 104.2 kJ(.)mol(-1), A = 1.12 x 10(7) s(-1) respectively. (c) 2005 Elsevier B.V. All rights reserved.