We wish to report that cobalt exchanged ZSM-5 has remarkably high hydrothermal stability, especially in comparison to Cu-ZSM-5. Calcination of Co-ZSM-5 in 2% water vapor at 750-degrees-C for a period of 99 h has a modest effect upon its activity for nitrous oxide decomposition. Treatment of Cu-ZSM-5 under the same conditions dramatically reduces the performance of the copper exchanged zeolite.