The inclusional complexation between alpha-cyclodextrin (alpha-CD) and 6-bromo-2-naphthol (BN) in aqueous solutions is investigated by means of electronic absorption, induced circular dichroism, emission, and H-1 NMR spectroscopies. With stoichiometries of 1:1 and 2:1, alpha-CD forms inclusion complexes with BN. The room-temperature phosphorescence of BN in aerated aqueous solution is observed from a 2:1 alpha-CD-BN inclusion complex, whereas a 1:1 alpha-CD-BN inclusion complex does not phosphoresce at room temperature. No observation of the BN room-temperature phosphorescence in deaerated solutions without alpha-CD suggests that alpha-CD decelerates not only the oxygen-quenching rate but also the other deactivation rates of the triplet state of BN. Analyses of chemical shift differences in H-1 NMR signals of BN indicate that the first alpha-CD molecule accommodates an end substituting a Br atom on a naphthalene ring in BN and then the second alpha-CD molecule encapsulates the other end substituting a hydroxyl group on the same naphthalene ring to form the 2:1 alpha-CD-BN inclusion complex.