Ab initiomolecular orbital theory has been used to study the binary complex formed between the benzene and ClF molecules. The 4–31G and 6–31G** basis sets were employed and also electron correlation effects were assessed by second order Møller-Plesset perturbation theory with the 6–31G** basis set in singlepoint calculations at the SCF optimized geometry. Basis set superposition errors have been evaluated by the counterpoise correction method. It was found that the Cl-F subunit interacts with the π electrons of the benzene ring through the Cl end, and also that there is a significant deviation from theC6vsymmetry expected.