The Aurivillius-type sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅ or NBT) powders were prepared by two-step hydrothermal routes with starting chemicals containing Bi(NO₃)₃?5H₂O, Ti(C₄H₉O)₄ and CH₃COONa?3H₂O. Crystalline phase and morphology of hydrothermally derived powders are investigated by XRD and SEM, and microstructure and electrical properties of derived ceramics are measured. The results indicate that the elemental ratio in the composition of hydrothermally derived nanopowders is very close to stoichiometic ratio of NBT, which possessed an average diameter of about 1.0μm and a thickness of less than 100 nm. The synthesis temperatures of NBT nanopowders are as low as 260～270℃, which is the lowest temperature among those published literatures. Compared with NBT ceramics by solid state sintering process, the ceramics resulting from hydrothermally derived powders, with dense ceramic body and fine grain size (<2μm), have very similar Curie temperature (≈674℃) and improved dielectric properties at high temperature.