The double perovskite Sr₂MgMoO₆ (SMMO) has attracted the attention to be used as SOFCs-anode because, despite its poor electrical conductivity, it exhibits high electrocatalytic performance for H₂-oxidation, sulphur tolerance and thermal stability. This mixed oxide provides multiple positions for doping (Sr, Mg and Mo-sites) and promotes oxygen vacancies formation, which allows to improve its properties such as chemical stability, electrical conductivity, etc. In present work, the Mo-site of SMMO was doped with Ni, in order to gain understanding of the structure, chemical and electrochemical properties of Sr₂MgMo_0.9Ni_0.1O_6-δ (SMMNi). The undoped sample (SMMO) was tested to comparison. The SMMNi and SMMO powders were synthesised by combustion method and thermally treated in air at 1000 and 1100 ºC respectively during 12 h. These materials were characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). XRD patterns for SMMNi powders confirmed the formation of a well-defined double perovskite phase belonging to the space group I-1. TEM micrographs show that SMMNi powders had a mean grain size around 340 nm. The surface analysis of SMMNi and SMMO powders were carried out by XPS on as-synthesised and post-reduced at 800 ºC in 10%H₂-Ar for 10 h. Results demonstrated that Mo⁶⁺ ions in SMMNi had been reduced to Mo⁵⁺after calcined in 10%H₂-Ar. Furthermore, XPS spectra exhibited no apparent change in oxidation state of Nickel after subjecting to SMMNi-powders to a reducing atmosphere. The stability studies indicate that SMMNi is more unstable in comparison to SMMO, under 10%H₂-Ar. Whereas SMMO remains stable until 1000 ºC, SMMNi decompose above 900 ºC. Additionally, electrochemical impedance spectroscopy (EIS) measurements on symmetrical SMMNi/GDC/SMMNi under reducing atmosphere at 700 ºC allowed seeing the influence of the time and environment conditions (H₂ content) in the anode polarisation resistance (R_pa). The aforementioned could be seen in Fig. 1, where the R_pa decreases from 3 to 0.4 Ωcm^-2 as pH₂ increases from 0.05 to 1 atm. These values are up 5 times higher than those for SMMO in the same conditions.