Oxygen vacancies in Na0.5Bi0.5TiO3 are of high demand as they stimulate the ionic conductivity essential to solid fuel cell applications. However, their available concentration, which is directly related to introduced A-site vacancies, is very limited. The objective of the present research is to study how the concentration of A-site vacancies may be increased by forming solid solutions with Sr0.7Bi0.2TiO3. A thorough study of heterogeneity and chemical composition of (1-y)Na0.5Bi0.5TiO3-ySr0.7Bi0.2TiO3 ceramics on a local level is conducted and accompanied by impedance measurements. It is shown that the chemical composition of the matrix grains is stable and follows the designed formula, allowing formation of A-site vacancies in a wide concentration range and, in limited amount, also oxygen vacancies. Inclusions, the content and character of which depend on Sr0.7Bi0.2TiO3 concentration, are detected and discussed. Complex impedance studies suggest that the compositions with y < 0.5 preserve low ionic conductivity up to 600–700 °C, but it significantly increases at higher y.