MgO addition in LiNbO3 single crystals is being actively studied for the usage in optical waveguides because of the resistance against optical damage. MgO was added as a dopant during the powder preparation of LiNbO3. Ti films were prepared by e-beam evaporation at room temperature on the mechanically polished Z surface of MgO-doped LiNbO3 crystals. After Ti him deposition, Ti was in-diffused by annealing. It was observed that Ti diffusion characteristic is strongly influenced by annealing temperature. During Ti diffusion, Li which was influenced by Ti diffusion, diffused out. In the case of Mg, however, its behavior was different from those of Ti and Li, and Mg made an accumulation layer near the surface of LiNbO3,