Abstract: The order of the activity of 5 aromatic and heteroaromatic compounds towars electrophilic substitution reaction was determined,namely,anthrac-ene-thiophene>naphthalene>benzene>pyridine.CNDO/2 calculations show that the activity order and the orientation of aromatic and heteroaromatic compounds towards the electrophilic substitution reactions were not determined by the charge distribution,but by the π-electron polarizability (superdelocalizability) of the reaction sites.