Biodiesel is always blended with petroleum diesel to serve as the transport fuel, to obtain the specific impact of petroleum diesel addition on thermal degradation for biodiesel; in this study, the thermal degradation characteristics of biodiesel and biodiesel blends with diesel are investigated by thermogravimetric analysis at heating rates of 10, 15, and 20 K min(-1) in the temperature range of 298 to 873 K. The kinetic parameters of activation energy are calculated based on the iso-conversional method, namely the Friedman method and Flynn-Wall-Ozawa method, and the reaction order is determined by Avrami theory. In addition, the thermodynamic parameters of enthalpy, entropy, and Gibbs-free energy are also calculated.