The grain boundary plays an important role in the electrical behaviors of solid oxide electrolytes for solid state fuel cells. To reveal the relationship between the structure and the ionic conductivity of grain boundary, the conductive properties of {1 1 1} and {1 1 0} twist grain boundaries in 8 mol%yttria-stabilized zirconia have been examined. These boundaries have a series ofΣvalues defined by the coincident site lattice model. It has been found that the activation energy of{1 1 1}twist grain boundary increases and then decreases with theΣvalue, while that of the{1 1 0}boundary shows an opposite trend. It is suggested that the properties can reflect the balance of the effects of lattice mismatch on the diffusion ability of oxygen vacancies and the segregation of oxygen vacancies and Y3 t ions. Therefore, the properties in polycrystalline electrolyte can be adjusted by controlling the grain boundary structures.