The inclusion complexation of aromatic amines with cucurbit[6]uril (CB[6]) capped with alkali metal cations was studied spectrophotometrically. We showed that CB[6] capped with alkali metal cations forms a 1:1 inclusion complex with the aromatic amine guests (neutral organic molecules), independent of the length of guest molecules. The effects of salts on the inclusion constants of CB[6] in the presence of different alkali salts were examined and it was found that the inclusion constants increased in the order of alkali cation Cs+ < Na+ < K+, suggesting the interaction of amine guests with the capped alkali metal cation. Further, the structures of the inclusion complexation of aromatic amines with CB[6] were characterized by H-1 NMR measurements. Based on the results, the inclusion abilities of CB[6] capped with alkali metal cations are discussed.