The kinetics of contact thermooxidation (CTO) of a polyethylene layer on a steel surface in connection with the change of peel strength (A) under conditions of free access of oxygen through the polymeric layer was studied. The CTO parameters (oxygen uptake, carbon dioxide evolution, change of carbonyl group content, change of the weight of the layer) and the change in the values of A were found to be kinetically interrelated. The dependence of the rate of change of individual CTO parameters and the magnitude of A on the thickness of the layer being oxidized and temperature can be described by a simple equation. The analysis of constants in this equation allows one to estimate the catalytic effect of the substrate in CTO. The dependence of experimental determined A values on contact time can be satisfactorily described by a simple expression based on the assumption that the magnitudes of A are controlled by two main competitive processes: the accumulation of oxygen-containing groups and oxidative cross-linking, causing the increase of A values, and reactions of oxidative destruction causing the decrease in A.