Multiwall　and　singlewall　carbon　nanotubes　were　used　as　precursors　for　preparing　metal　ion-decorated　nanotubes.　The　activated　nanotabes　catalyze　metal　deposition　specifically　onto　their　surfaces　upon　wetting　the　surface　of　nanotubes.　K+,　Cu2+,　Mg2+,　Ca2+　and　Fe　decorated　singlewall　and　multiwall　carbon　nanotubes,　were　screened　for　the　catalytic　activity　in　reactive　violet　dye　waste　water　decomposition　reaction　under　ionizing　irradiation.　It　showed　that　K+　Mg2+,　Ca2+　decorated　multiwall　carbon　nanotubes　have　higher　catalytic　activity　than　others　under　different　condition,　such　as　basic　and　acid　condition,　and　different　concentration.　The　catalytic　active　of　decorated　nanotubes　was　improved　highly　at　very　low　dose.