We have deposited diamond-like carbon (DLC) films by radio-frequency magnetron sputtering, and have annealed the films under various conditions to investigate the effects of annealing on the structural properties by visible Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. The structural ordering of hydrogenated DLC films occurs during annealing below 400 degrees C in a vacuum and a hydrogen gas atmosphere, while unhydrogenated DLC films are not ordered during annealing even at 700 degrees C. On the other hand, the ordering and the decrease of the sp(3) content are observed for both the films after annealing under an atomic hydrogen exposure. The ordering progresses as the annealing temperature and time are increased. The! reduction of the film thickness after annealing is suppressed with increasing annealing temperature. The results suggest that both the preferential etching by atomic hydrogen and the hydrogen evolution encourage the structural changes under an atomic hydrogen exposure. (c) 2006 Elsevier B.V. All rights reserved.