Barium-nitride-hydride is one of the few documented H--ionic conductors. It crystallises in the alpha-NaFeO2-structure (space group R3mBAR) with distorted Ba-Octahedral centred alternately by H- and N3-. Neutron diffraction shows that the hydrogen ions are distributed independent of temperature over two lattice sites : 85% on (3a) and 15% on (6c). At T>525 K a sharp increase of the ionic conductivity can be observed. The diffusion process takes place by uncorrelated jumps of hydrogen ions between regular lattice sites. Using quasielastic neutron scattering techniques and a planar jump diffusion model, we were able to determine the mean residence time tau on a H--site to be tau = 20 +/- 2 ps and the diffusion constant D to be 2.1 +/- 0.3 x 10(-5) cm2/s at T = 823 K.