Oxygen nonstoichiometry and electrical conductivity of LaSrNiO4-delta nickelate were investigated and oxygen permeability of LaSrNiO4-delta + 40% Ag composite ceramics was estimated. The oxygen content in LaSrNiO4-delta changes from 3.99 to 3.45 in the temperature range 600-1000 degrees C at oxygen partial pressures 100 to 2 Pa. The decrease of oxygen content in nickelate takes place by removing it from vertexes of NiO6 octahedrons which form the perovskite layers within the lattice of nickelate. This causes an increase of the c parameter and a decrease of the a parameter of the tetragonal cell of nickelate. The cell volume of the crystal remains constant. The nickelate studied appeared to be p-type conductor with a metallic-like temperature function of the electrical conductivity. At the same experimental conditions the oxygen permeability of LaSrNiO4-delta + 40% Ag composite is lower by a factor of 100 in comparison with the permeability of La2NiO4+/-delta and La2NiO4+/-delta + 40% Ag composite.