Ionic doping effects of various ions in Bi-layered ferroelectric SrBi2Nb2O9 (SBN) ceramics were studied. Un-doped and doped SBN ceramics with Ba2+, Pb2+, Ca2+, Bi3+, La3+, Ti4+, Mo6+, and W6+ ions were made with solid state reactions. Temperature dependent dielectric constants were measured. Ferroelectric transition temperature (TC) decreased with Ba2+ and Pb2+ ions but increased with Ca2+ ion which substitutes the 12-coordinated Sr2+ site. TC increased with Ti4+, Mo6+, and W6+ ions which substitute the 6-coordinated Nb5+ sites. With trivalent Bi3+ and La3+ ions, TC increased with Bi3+ ion but much decreased with La3+ ion. These results showed that the ion size plays an important role in ferroelectricity of SBN ceramics.