A series of benzimidazole and benzimide model compounds were oxidatively degraded at high temperatures (350-600°C). All of the compounds degraded to small fragments, i.e., carbon oxides, cyanogen (trace), and water, as well as condensable materials such as nitriles and anhydrides. The most outstanding feature of the degradation was the origin of these latter pyrolysis products; in each case they originated from the acid portion of the molecule. Nitrogen was noticeably absent in both the gas phase and the condensable degradation products except as nitrilo-moieties. Poly-2,2′(m-phenylene)53′-bibenzimidazole produced similar products. The proposed mechanism invokes a preferential attack by oxygen at the aminobenzenoid rings.