Neodymium nickelates Nd2Ni1-xO4+δ with Ni non-stoichiometry, varied in a wide x range of 0.0–0.08, are synthesized for the first time, and their properties are studied depending on the Ni content. The limit of Ni deficiency is found to reach 6%. According to the XRD data, the materials of the Nd2Ni1-xO4+δ series are single-phase in the range of x from 0.0 to 0.06 and exhibit an orthorhombic structure with a Fmmm space group. Results of the TGA-DSC studies shows that the temperature of the Fmmm – I4/mmm phase transition changes insignificantly (up to ∼5 °C), thus does not depend on Ni non-stoichiometry. The Raman scattering studies reveal that at low Ni deficiency the Raman spectra are typical for the Ni-stoichimetric oxidized (δ ≈ 0.2) Nd2NiO4+δ. While at the limiting value of x equal to 0.06, the lattice disorder and [NiO6] octahedral distortions reach a maximum feasibility with Ni–O1 vibrations getting involved into Raman scattering. The highest total conductivity (101 S/cm at the maximum) is observed for the sample with x = 0.02, which shows a more pronounced second-order overtone at 800–930 cm−1 in Raman scattering. This material can be recommended for further studies and possible electrochemical applications as the most prospective in the series due to its superior electrical properties.