Polycrystalline La 1.2 Sr 2.7 RuO 7+δ has been synthesized by standard ceramic techniques. The powder X-ray diffraction data of this phase, in which ruthenium is in a pentavalent state, has been indexed in the trigonal space group R3¯m, with cell constants a=5.750(1) Å and c=18.349(3) Å. Along the c-axis, the structure can be described in terms of uniform stacking of two AO 3 layers and one A 2 O 1+δ layer (A = La/Sr). The A cations in the A 2 O 1+δ layer are trigonal-prismatically coordinated and the Ru ions occupy the octahedral sites between the AO 3 layers. La 1.2 Sr 2.7 RuO 7+δ is a new n=2 member of the general family of [A 2 O 1+δ ][A n B n−1 O 3n ] hexagonal perovskites with n representing the number of AO 3 successive layers. δ was found to be approximately 0.35. Synthesis, XRD–Rietveld analysis, thermogravimetric investigations, XANES spectroscopy and magnetic behavior of this compound are discussed.