A convenient method for the preparation of benzimidazole carboxaldehydes by the oxidation of methylbenzimidazoles with cerie ammonium nitrate is described. A series of methyl, dimethyl, and trimethylbenzimidazoles was treated with ceric ammonium nitrate in sulfuric acid, and the major ethyl acetate soluble products were characterized. In addition to carboxaldehyde products, side reactions yielding benzimidazolediones and nitrobenzimidazoles were also observed.