The aromaticity of six-membered rings with six pi electrons was studied by CiLC (CI/LMO/CASSCF) analysis on the basis of ab initio molecular orbital methods. The aromaticity was defined for equivalent electronic states for each bond and the gap between the weights of the singlet coupling and polarization terms. These weights were calculated for the aromatic structure (D-6h) of C6H6, Si6H6, B-6, Al-6, N-6, and P-6, and it was revealed that the aromaticity is closely related to the electronegativity of the composed atoms. The definition of aromaticity employed here corresponds to resonance concepts.