Abstract: The ion-molecule reactions of disubstituted benzene with ion system of acetyl chloride under chemical ionization condition were examined and the fragmentation reactions of the adduct ions formed by the ion-molecule reactions were studied by using collision-induced dissociation technique.It was found that the electron-releasing groups favored the adduct reactions and the electron-withdrawing groups did not.The position and properties of substituted groups affected the relative abundance of the adduct ions.The fragmentation reaction of the adduct ion formed by orthobenzene diamine with acetyl ion was similar to the reductive alkylation reaction of amine in condensed phase.