Hydrogen chemisorption at initial stage occurred only at certain atomistic configuration, with calculated energy barrier for the absorption and the energy of reaction for the H-2 dissociation being 0.89 eV and -0.11 eV, respectively. Pre-absorbed H atoms could act as autocatalysts for further dissociative chemisorption of H-2 at higher coverage. Up to 100% coverage ( corresponding to hydrogen uptake of 5 wt%) of hydrogen chemisorption was energetically favorable, but might result in tube deformation. It is interesting to note that single H atom chemisorption introduce spin-polarized magnetic moments to hydrogenated AlNNTs. (C) 2008 Elsevier B. V. All rights reserved.