A kind of functional polysiloxane containing pendent gamma-chloropropyl groups,alpha,omega-trimethylsiloxy-poly(methylchloropropyl)siloxane (PMCPS), was synthesized. Its thermal stability and thermal degradation kinetics were studied through thermogravimetric analysis (TGA) in nitrogen atmosphere. The effect of the introduced gamma-chloropropyl units on the thermal degradation behavior of PMCPS was discussed. The TGA revealed that PMCPS exhibited three degradation stages in the temperature range of 30-800 degrees C. The depolymerization of the main chain of polysiloxane was accelerated by introducing the gamma-chloropropyl groups. Two isoconversional methods, the Friedman and the modified Kissinger-Akahira-Sunose (KAS) by Starink, were chosen to investigate the thermal degradation kinetics of PMCPS. The average activation energies of the thermal degradation of PMCPS obtained from the two methods were compared and found to be in good agreement with each other.