The effect of Zn2+ substitution on the electrochemical performance and the structural evolution upon cycling of Na3Ni2SbO6 and Na3Zn0.5Ni1.5SbO6 is reported. Samples were synthesized by solid state route and characterised by ex-situ X-ray diffraction and ex-situ 23Na solid state NMR, the results show that the partial substitution of Ni2+ by Zn2+ alters the superstructure symmetry and leads to a disordered lattice. This structural reorganisation has direct consequences on the electrochemical performances of Na3Zn0.5Ni1.5SbO6 with an average voltage of ∼3.3 V and with a specific capacity increase up to 145 mAh.g−1 at C/10. We observe that Zn2+ cations are inhomogeneously distributed in the structure, leading to different Na+ environments which are characterized by NMR. The phase transitions observed at high voltage in Na3Ni2SbO6 are suppressed in Na3Ni1.5Zn0.5SbO6 resulting in a smooth electrochemical profile with a low polarization. The presence of an irreversible phase at the end of the discharge was also detected in the undoped material.