Deuterium (D) induced cracking (DIC) of Ti was in-situ investigated by the hot stage microscope (HSM) technique combined with the pressure-volume-temperature (PVT) method. Only several cracks were observed on the surface of Ti upon exposure of D2 at 550℃, while more unique circular cracks appeared when Ti was heated from room temperature up to 550℃ in the D2 atmosphere. The morphology changes of Ti induced by deuterium during heating is consistent with the characteristics described by the preferred edge-attack model. X-ray photoelectron spectroscopy (XPS) measurements indicated that the surface passivation layer on Ti, mainly consisting of titanium oxides, carbides and nitrides, played an important role in the formation of circular cracks.