Due　to　their　unique　physical　properties,　carbon　nanotubes　are　becoming　promising　novel　materials　in　diverse　areas　like　information　technology,　ultrastiff　materials,　biomedicine　etc.　The　toxicological　study　of　these　materials　is　very　imperative　for　the　safety　assessment　in　respect　to　their　wide　applications.　The　objective　of　the　toxicity　study　was　to　find　out　whether　water　soluble　multi-walled　carbon　nanotubes　(S-MWNTs)　would　impair　the　phagocytic　activity　of　macrophages,　which　play　an　important　role　in　defenses　against　invading　microbioles.　The　results　showed　that　S-MWNTs　did　not　impair　the　phagocytosis　of　macrophages;　to　our　surprise,　S-MWNT　significantly　enhanced　this　function.　Increased　activity　of　enzymes　in　lysosome　also　showed　that　S-MWNTs　enhanced　the　lysosome　function　of　macrophages.　However,　S-MWNTs　can　not　influence　nitric　oxide　secretion　in　macrophages　and　induce　inflammation.