Samples of Ti and Zr metals have been carbonized or nitrided at high temperature by means of reactive plasma processing. Thickness and hardness of modified layers increased with the processing temperature and time in an experimental range below 1500°C for less 5h. The maximum hardness of TiC-layer modified at 1300°C for 3h was about 5000Hv(kg/mm2) and the maximum thickness of ZrC-layer formed at 1400°C for 5h reached about 100μm. A TiC-layer was analyzed with EPMA, XRD, EXAFS and PAS(Positron Annihilation Spectroscopy). It was confirmed that the sub-surface layer of Ti metal was the mixture of TiC ceramics and Ti metal, and that the thickness of TiC with NaCI type structure was very large.