Nanotube rings were fabricated with a high yield by heating the lightly etched c arbon nanotubes under ambient conditions that were produced by chemical vapor deposition method. These rings, typically 300nm in diameter, were characterized using atomic force microscopy, transmission electron microscopy and scanning ele ctron microscopy. The structure and yield of nanotube rings depended strongly o n the heating temperature and time. Our researches suggest that the optimal heat ing temperature ranges from 510 ℃ to 530 ℃, and that the heating time up to 1 20 min is favorable for the increase of the yield. At high temperatures, the est erification of carboxyl functional groups attached at the nanotube ends resulted in the bending of straight nanotubes into closed rings.