Atomistic mechanisms that restrain diffusion of oxygen vacancies in BaTiO3 doped with rare earth ions as donors were analyzed using molecular dynamics simulation. It was confirmed that formation of cation vacancies and reduction of lattice volume are sources of resistance for the diffusion. The cation vacancies trap the oxygen vacancies at the nearby O2- sites by an attractive force associated with Coulombic interaction. In contrast, the rare earth ions repel the oxygen vacancies, which migrate via O2- sites, and accelerate the diffusion. This is one of the factors that determine the restraint behavior of the diffusion, which depends on the type of rare earth ion in BaTiO3-based materials.