Structures of protonated AlXH2 and AlX2H (AlXH3+ and AlX2H2+) and their dihydrogen complexes AlXH5+ and AlX2H4+ (X = F, Cl, and Br) were investigated using the ab initio method at the G2 level of theory. All the dihydrogen complexes involving hypercoordinated aluminum atom with a three-center two-electron (3c-2e) bond. The G2 calculated protonation energies of AlXH2 and AlX2H to form AlXH3+ and AlX2H2+, respectively, were found to be highly exothermic. The possible dissociation of the cations AlXH5+ and AlX2H4+ into AlXH3+ and AlX2H2+ and molecular H-2, respectively, are calculated to be endothermic.