The deformation behavior and the failure mechanism of the diamond-like carbon (DLC) film/Ti-6Al-4V substrate have been investigated by lateral force measurement on a nanoindentation instrument. It was found that deformation proceeds can be divided into three stages: at the low load regime, the film fully recovers; then, with the increase of the scratch load, a fish bone like trace with tiny cracks along the track of the indenter is produced due to the stress concentration at the two front edges of the indenter tip; finally, as the scratch load is increased to a critical value, where the elastic deformation is equal to the plastic one, plough damage occurs with film spallation. The results revealed that the plough damage might originate from the tiny cracks of the fish-bone trace. A model has been proposed on the basis of the results observed; suggesting that the delamination of the diamond-like carbon film from the substrate is due to the interaction of the parallel cracking in the film as well as the partial separating of the interface between the film and the substrate. (C) 2004 Elsevier B.V. All rights reserved.