Ferroelectric properties of SrBi2Ta2-xNbxO9 (SBTN) thin films were affected by the amount of Bi content in SBTN. The addition of Bi into the SBTN films could be accomplished by heat treating the SBTN/Bi2O3/SBTN heterostructure fabricated by the rf magnetron sputtering method. The Bi content was controlled by changing the thickness of the sandwiched Bi2O3 from 100 to 400 Angstrom in the SBTN/Bi2O3/SBTN heterostructure. A Bi2Pt phase was formed as a second phase in the SBTN films inserted with 400 Angstrom Bi2O3 layers, resulting in poor ferroelectric properties. A Bi2Pt phase was formed by the reaction between the bottom Pt layer and the SBTN layer. It is found that the Bi2Pt phase formation depends on the annealing temperature and Bi concentration. By inserting the Bi2O3 layers between the SBTN films, the crystallization temperature and the grain growth temperature was also reduced.