The results of non-isothermal kinetic analysis of the thermo-oxidative degradation in air and in oxygen of the low density polyethylene (LDPE) are presented. It was observed that similar processes take place at thermo-oxidative degradation in air and in oxygen. The first process, which leads to solid products, is followed by thermo-oxidative degradation with generation of volatile products. It was shown that the first process of thermo-oxidation occurs at lower temperatures in oxygen than in air. The kinetic analysis of this process, performed using Kissinger method, shows that the pre-exponential factor (A) depends on the partial pressure of oxygen (P) according to the relationship: A = A(0)P(delta), where A(0) and delta are material constants.