We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr 2 LnMoO 6 (Ln=Eu, Gd, Dy, Ho, Er, Yb) with Mo 5+ and Ln 3+ electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo 5+ cations. Structural characterization by XRPD and NPD was performed when Ln=Ho, Er, Yb and just XRPD for absorbing Ln=Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P2 1 /n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25K and the determined effective magnetic moments are consistent with those expected for the pair Ln 3+ –Mo 5+ . All the phases have negative values of the Weiss temperature indicating dominance of antiferromagnetic interactions.