Many of the applications of diamonds expose them to high temperatures and atmospheres containing oxygen. Under these circumstances two important phenomena responsible for the thermal damage of diamonds are: oxidation and graphitization. It is well known that coatings on diamonds provide a better performance, but the amount of information in literature about the protective mechanism of these coatings is very scarce. The present work proposes a study about the thermal damage effect on diamonds with titanium (Ti) coating comparing with diamonds without it. Samples of uncoated diamonds and Ti- coated diamonds were heat treated at 1200 °C during different periods of time and characterized prior to and after the treatments. Differential thermal analysis (DTA) was performed to observe the temperatures that transformations in diamonds occur. The analysis of phases present in the samples and the observation of new phases formed were carried out by means of X-ray diffraction (XRD). In order to observe the diamond surface and how the chemical elements are distributed in it, the samples were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results prove the protective capability of the Ti coatings, clarifying the protective mechanism against the thermal damage.