Tritium has been introduced into three coal tar pitches and a naphthalene pitch by two methods, one by isotope exchange with tritiated water using Pt/Al2O3 catalyst, and the other by hydrogenation with tritiated gaseous hydrogen using Ni-Mo/Al2O3 catalyst. The tritium-labelled pitches were carbonized up to 1000-degrees-C under nitrogen atmosphere. The release behaviors of hydrogen and tritium during the carbonization of tritiated pitches were investigated by comparing the rates of dehydrogenation and detritiation. The results indicate that the hydrogen introduced into the pitch by the isotope exchange is released more rapidly than the original hydrogen in the pitch while the hydrogen introduced into the pitch by the isotope addition is slightly more difficult to release relative to the original hydrogen in the pitch during the pyrolysis of the pitch. Moreover, it was clarified that the extent of development of optically anisotropic texture of the pitch is related not to the hydrogen exchange ratio but to the rate of hydrogen release during pyrolysis.