Reactivity　is　of　great　importance　for　metal　nanoparticles　used　as　catalysts,　biomaterials　and　advanced　sensors,　but　seeking　for　high　reactivity　seems　to　be　conflict　with　high　chemical　stability　required　for　metal　nanoparticles.　There　is　a　subtle　balance　between　reactivity　and　stability.　This　could　be　reached　for　colloidal　metal　nanoparticles　using　organic　capping　reagents,　whereas　it　is　challenging　for　powder　metal　nanoparticles.　Here,　we　developed　an　alternative　approach　to　encapsulate　copper　nanoparticles　with　a　chemical　inertness　material　-　hexagonal　boron　nitride.　The　wrapped　copper　nanoparticles　not　only　exhibit　high　oxidation　resistance　under　air　atmosphere,　but　also　keep　excellent　promoting　effect　on　thermal　decomposition　of　ammonium　perchlorate.　This　approach　opens　the　way　to　design　metal　nanoparticles　with　both　high　stability　and　reactivity　for　nanocatalysts　and　their　technological　application.　©　2015,　Nature　Publishing　Group.　All　rights　reserved.