A process is provided to produce N-phosphonomethylglycine by the oxidation of N-phosphonomethyliminodiacetic acid to form an intermediate N-phosphonomethyliminodiacetic acid-N-oxide with a peroxide in the presence of an effective amount of a catalyst selected from the group consisting of water-soluble tungsten compounds and a mixture of water-soluble tungsten compounds and a water-soluble molybdenum compound to form the intermediate, and thereafter converting the intermediate N-phosphonomethyliminodiacetic acid-N-oxide to N-phosphonomethylglycine.