The purpose of this work is to improve adhesive strength of Ti doped DLC films by heat treatment in vacuum. The films have been prepared on silicon substrates by DC magnetron sputtering using C and Ti target in Ar plasma. The amount of Ti has been changed with the input electric power to Ti target from 0 to 200W. The adhesive strength of DLC film and Ti doped DLC films were measured by scratch tests. The adhesive strength of DLC film was decreased by the vacuum heating. On the other hand, that of the Ti doped DLC films was improved irrespective of the deposition conditions. Especially, the heat treatment was most effective for the film containing large amount of Ti to improve the adhesive strength, and that became larger above two times after the heat treatment.