Nickel zinc manganite Mn2.35-xNi0.65ZnxO4 powders were investigated by X-ray and neutron diffraction experiments. The variation of the cell parameters determined from X-ray data was used to get an estimate of the cationic distribution. Neutron diffraction experiments were performed to obtain room-temperature structural parameters, the tetrahedral and octahedral average scattering lengths and the oxygen-cation distances. Because of the opposite signs of the scattering lengths (b(Mn) and b(Zn)), the neutron data allow to determine, with high precision, the concentration of the cations on the different sites of the spinel structure. The cationic distribution determined from these data indicated that a small part of the Zn2+ cations occupy the octahedral sites, for zinc-rich oxides (x > i).