Non-isothermal kinetics of solid-state decomposition of polybisphenol-A-carbonate [PC; Mn; 1,5 - 3.68 ? 104) and polymethyl metacrylate (PMMA Mn : 1.55 - 3.52 ? 104] has been investigated under nitrogen atmosphere in view study the effect of molecular on their themal decompositions in solid state. Thermal data deduced through simulthanous thermo gravimetric differential thermal analysis-differental thermo gravimetry [TG-DTA-DTG] was used for calculations of thermodynanmic paramerters through Horowiz-Metzger and coats-Redfern methods, kinetics and mechnaism of degradations of each polymer at different molecular masses-[PC] showed two step decompoisition in general.Horowiz-Metzger, coats-Redfern methods have shown greater values of energy of activations than coats-redfern methods for [PC] backbone porvidee a wide difference in fluency factor but almost same entropy change in most of the cases. Thermodynamic and kinetics data were mostly satisfied for first entropy change in most of the cases. Thermodynamic and kinetics data were mostly satisfied for first order and zero kinetics in case of [PC] whereas were not satisfactory for [PMMA]