Strontium niobates with different crystalline structure and morphology have been prepared via a hydrothermal method and applied as a support for ruthenium catalyst in ammonia synthesis. The sample synthesized with a nominal Sr/Nb = 2.0, having a pure Sr2Nb2O7 crystalline phase and specific surface area of 87 m(2) g(-1), exhibits the best performance as support for Ru catalyst. The flake-structured Sr2Nb2O7 substrate induced epitaxial growth of truncated pyramid shaped ruthenium nanoparticles with a dispersion as high as 93%, which have abundant steps and B-5 sites playing a key role in ammonia synthesis catalysis. Adding Cs- or Ba-promoter enhanced the activity of Ru/Sr2Nb2O7 catalyst drastically. The highest ammonia synthesis rate over 8Cs- or 4Ba-2 wt%Ru/Sr2Nb2O7 was 4986 and 2317 (mu mol g(cat)(-1) h(-1)) at 0.1 MPa and 673 K, respectively. In addition, both catalysts were stable over reaction for 72 h at 673 K and 0.1 MPa. Thus, the synthesized Sr2Nb2O7 is expected to be a practically promising oxide support for ruthenium ammonia synthesis catalsyts.