The unified multichannel positron annihilation model in humidity-sensitive nanoporous MgAl 2 O 4 ceramics with a spinel structure was generalized. It is shown that this model unifies the channels of positron trapping and ortho-positronium decaying. Within this approach, the first component in the lifetime spectra reflects microstructure specificity of the spinel structure with character octahedral and tetrahedral cation vacancies, the second component responsible to extended defects near intergranual boundaries and the third component correspond to" pick-off" annihilation of ortho-positronium in the water-filled nanopores of ceramics.