B-C-N nanotubes prepared by a flush evaporation method using a dc arc 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-, and carbon or carbon nanotubes surrounded with boron nitride nanotubes. These types of nanotubes were obtained at higher temperatures than about 3000 K, however, these were not formed at lower temperatures than about 3000K. On the other hand, nanocapsules were formed at all the experimental temperatures and nanocapsules with a homogeneous phase were obtained at lower temperatures than about 3000 K. The effect of additives on the formation of B-C-N nanotubes was not clear. Based on these experimental data depending on temperatures and corresponding microstructures, the formation mechanisms of both nanotubes and nanocapsules were briefly discussed.