This article illustrates several examples of self-assembled multi-phase nanostructures found in the nanotubes and nanoparticles in the BCN ternary system. Spatially resolved EELS is proved to be an efficient technique to diagnose such composite nano-structures. Examples cover wide range of specimens: carbon nanotube with boron or nitrogen, BN/C composite nanotube and BN/C nanobox. These composite nanotubes and nanoparticles can be prospects for the future nanodevices.