Conjugation between sigma- and pi-aromatic moieties in 1-C-arylated monocarba-closo-dodecaborate anion derivatives 2 has been identified by means of kinetic experimental studies combined with theoretical calculations. We found that the reaction rate of iodination at the 12-B vertex of the carborane anion cage was affected by distal substituents on the benzene ring connected at the antipodal carbon vertex. Hammett and Yukawa-Tsuno plots indicated that substantial resonance effects are involved. Density functional theory calculations enabled detailed interpretation of the electronic interaction.