In this paper we have studied the kinetics of the thermal decomposition of scrap tire using nonisothermal thermogravimetric methods. Experiments were carried out over the temperature range of 20-600 degrees C at different heating rates and with various powder sizes. Under the conditions studied, the heating rate has a significant effect on the pyrolysis process while the powder size has little effect on it. The results indicated that the pyrolysis process of tire powder consisted of three stages which are related to the degradation of different tire materials. Two models were developed to simulate this pyrolysis process and to determine the kinetic and process parameters. The predictions by the two models agree well with experimental data.