Thermal decomposition kinetics of low- and high-density polyethylene (LDPE, HDPE) were investigated. Thermal degradation of raw and waste LDPE and HDPE was performed using a thermogravimetric analyzer (TGA) in nitrogen atmosphere under non-isothermal conditions. Heating rates between 5 and 50 K/min were employed in TGA experiments. First-order decomposition reaction was assumed, and for the kinetic analysis an integral method was used. The apparent activation energy (E-a) and the pre-exponential factor (k(o)) were evaluated. It was found that value of the kinetic parameters and apparent activation energy of HDPE were larger than the LDPE.