Thin film of both A- and B-site co-substituted Sr 0.8Bi 2.2Ta 2O 9 (SBT) by Pr 3+ and Nb 5+, i.e. Sr 0.8Pr 0.1Bi 2.1Ta 1.5Nb 0.5O 9 (SPBTN) was fabricated on Pt/Ti/SiO 2/Si substrates by metalorganic decomposition method. The Nb 5+ substitution at B-site and Pr 3+ substitution at A-site enhanced the remanent polarization and reduced the coercive field of the films, respectively. The remanent polarization (2 Pr) value of the SPBTN film was 22 μC/cm 2. The coercive field (2 Ec) value of the SPBTN film was 102 kV/cm, which was much lower than that of SBTN (165 kV/cm). The effects of substitution on structural and ferroelectric properties of SBT were discussed in detail. As a result, the A- and B-sites co-substitution may be one of the promising ways to improve ferroelectric properties of SBT.