B-C-N nanotubes prepared by a flush evaporation method using a d.c. are plasma were mainly characterized by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The nanotubes obtained were divided into three types, such as carbon-, boron nitride-, or carbon nanotubes surrounded with boron nitride nanotubes. These types of nanotubes were obtained at temperatures higher than approximately 3000 K; however, these were not formed at temperatures lower than approximately 3000 K. On the other hand, nanocapsules were formed at all the temperature regions, but the nanocapsules obtained were smaller at lower temperatures. The addition of nickel produced a bundle of single walled carbon nanotubes and boron nitride nanocapsules surrounding nickel particles. Based on the experimental data obtained, the formation mechanisms of both nanotubes and nanocapsules were discussed.