Thermal degradation processes are of great importance in the case of polyoxymethylene. Establishment of the mechanism of oxidative decomposition is particularly important, because it proceeds under conditions when depolymerization is predominant over oxidation. The basic kinetic regularities of thermal and thermal‐oxidative degradation of polyoxymethylenes have been determined, and differences have been observed; that depend on the chemical nature of endgroups. Thermal degradation proceeds as depolymerization with generation of active centers at the chain end for POM hydrate, and following the “random law” for end‐capped POM and copolymers. The “kinetic” chain is shorter than the “substance” one. Formaldehyde participates in chain transfer of POM degradation. A method has been proposed for determining the true activation energy of reactions that are more complicated due to heat transfer. The true E of POM for different end groups has been determined. The thermooxidative decomposition proceeds as depolymerization initiated by oxygen and follows the “random law.” Oxygen has an inhibiting effect by reacting with active centers of POM. The degradation rates and accumulation of formic acid depend on the nature of end groups, and HCOOH acts as an accelerator. The most probable sources of HCOOH were proposed, and the active centers of POM degradation are shown to be of a dual nature. The mechanism of degradation and some principles of stabilization are proposed.